This updates the documentation of automatic CE to EE merges to cover the
new automatic merging setup.

This sets up GitLab CI to automatically push CE master changes into EE
master, or revert them if the changes cause merge conflicts. The CI
configuration contains a single job to do this: `merge:master`. This job
is executed for every push to master, and periodically using a CI
schedule.

The periodic job is necessary because incremental jobs may not be able
to revert commits if newly added commits depend on these commits. By
re-running the job periodically (including all changes since a large
enough time frame), we can ensure that such commits are also reverted
(if they still conflict at that time).

The job runs in its own "merge" stage, _after_ the build and prepare
stages, but _before_ running the tests. This ensures that randomly
failing tests won't prevent code from being merged into EE. Running the
stage after the "prepare" stage reduces the chances of the job reverting
CE changes just because it ran before a corresponding EE MR was merged
into EE master.

Add echo so that we know which branch was taken

See merge request gitlab-org/gitlab-ce!23499

Fix unrelated deployment status in MR widget

Closes #54125

See merge request gitlab-org/gitlab-ce!23175

Update architecture.md

See merge request gitlab-org/gitlab-ce!23430

HTTPS for JupyterHub installation

See merge request gitlab-org/gitlab-ce!23479

reorder notification settings by noisy-ness

See merge request gitlab-org/gitlab-ce!23490

Updated Katex "Supported Functions" link

See merge request gitlab-org/gitlab-ce!23343

Change auto devops banner link path

Closes #54689

See merge request gitlab-org/gitlab-ce!23476

commit 04b06a2293fa12660a9c213a9db27fe90b83248b
Merge: d580841d4ed a445aa0a
Author: Shinya Maeda <shinya@gitlab.com>
Date:   Mon Dec 3 10:51:55 2018 +0900

    Merge branch 'master-ce' into fix-mr-widget-unrelated-deployment-status

commit d580841d4ed944f01e6417fa77842826843b6a04
Author: Shinya Maeda <shinya@gitlab.com>
Date:   Fri Nov 30 18:11:04 2018 +0900

    Add environment to all_models.yml

commit 689fbe2699a3adf10804312e680fa336e4560eaf
Author: Shinya Maeda <shinya@gitlab.com>
Date:   Fri Nov 30 17:00:35 2018 +0900

    Proper way to get uniq relationship

commit c0733c6ecd535a6a1b6243080a2226836890f479
Author: Shinya Maeda <shinya@gitlab.com>
Date:   Fri Nov 30 16:20:40 2018 +0900

    Revert build change

commit 19dc55a8fe6e0fa575858d51144516b7fb0120de
Author: Shinya Maeda <shinya@gitlab.com>
Date:   Fri Nov 30 16:19:18 2018 +0900

    Add uniq option

commit 0a6995f311c09b453fd0aecff2f6052de38efc27
Author: Shinya Maeda <shinya@gitlab.com>
Date:   Fri Nov 30 16:14:30 2018 +0900

    Drop persisted_environment

commit 3f68fc783b0ee0d66e03de6d979616c4c4892118
Author: Shinya Maeda <shinya@gitlab.com>
Date:   Wed Nov 28 13:59:04 2018 +0900

    Return empty array if pipeline is nil

commit 73801c5c3d06339e38dce7461a71285bcdbb8f45
Author: Shinya Maeda <shinya@gitlab.com>
Date:   Tue Nov 27 16:34:47 2018 +0900

    Add changelog

commit d461699abf2835cc51949a5138e829628209dd6d
Author: Shinya Maeda <shinya@gitlab.com>
Date:   Tue Nov 27 16:32:20 2018 +0900

    Squashed commit of the following:

    commit 77ab5259605e217a39b04d2cea6204277e42d2b5
    Merge: 7ac1ed50612 2ee8c40f
    Author: Shinya Maeda <shinya@gitlab.com>
    Date:   Tue Nov 27 16:31:07 2018 +0900

        Merge branch 'master-ce' into fix-mr-widget-unrelated-deployment-status

    commit 7ac1ed50612620df6408220b0a7cfcb626a04c48
    Merge: 49ba5c5aeff b55aeca2
    Author: Shinya Maeda <shinya@gitlab.com>
    Date:   Mon Nov 26 20:01:43 2018 +0900

        Merge branch 'master-ce' into fix-mr-widget-unrelated-deployment-status

    commit 49ba5c5aeff3efee7b7498d443372021c3f4f8b5
    Merge: aa3fd0ff9e8 fbbe5ccd
    Author: Shinya Maeda <shinya@gitlab.com>
    Date:   Mon Nov 26 15:27:36 2018 +0900

        Merge branch 'master-ce' into fix-mr-widget-unrelated-deployment-status

    commit aa3fd0ff9e8a418a233ebaa60b38c081cab50099
    Author: Shinya Maeda <shinya@gitlab.com>
    Date:   Tue Nov 20 18:28:53 2018 +0900

        Fix static analysis

    commit 7afe5f37003869a73dbb297229f8533f78b82684
    Merge: e65b9580ff4 8a581d53
    Author: Shinya Maeda <shinya@gitlab.com>
    Date:   Tue Nov 20 18:27:33 2018 +0900

        Merge branch 'master-ce' into fix-mr-widget-unrelated-deployment-status

    commit e65b9580ff422359113e1a4e37c212f7b13aba4d
    Author: Shinya Maeda <shinya@gitlab.com>
    Date:   Mon Nov 19 17:59:48 2018 +0900

        Ignore deployments from project import/export

    commit 9eb4ddab8415c1ef61a3c646bdc4602bcf4ebe24
    Author: Shinya Maeda <shinya@gitlab.com>
    Date:   Mon Nov 19 16:26:00 2018 +0900

        Add memoization

    commit 57f0bea3aaaa07b75d18e52068c532277350cda0
    Author: Shinya Maeda <shinya@gitlab.com>
    Date:   Mon Nov 19 16:21:39 2018 +0900

        Fix unrelated deployment status in MR widget

slightly improve readability

See merge request gitlab-org/gitlab-ce!23466

Bump gpgme gem version from 2.0.13 to 2.0.18

See merge request gitlab-org/gitlab-ce!23491

This should help debug issues like
https://gitlab.com/gitlab-org/gitlab-ce/issues/54760

fixes !54609

Upgrade GitLab Workhorse to v7.3.0

See merge request gitlab-org/gitlab-ce!23489

Add additional scope check to Todo#for_target spec

See merge request gitlab-org/gitlab-ce!23487

This works around a condition where the Issue and the MergeRequest
created by FactoryBoth both had the same ID, which caused `for_target`
to return two records when we only expected one.

Add documentation reference to gitaly-debug

See merge request gitlab-org/gitlab-ce!23386

Backport from gitlab-org/gitlab-ee!6878

See merge request gitlab-org/gitlab-ce!23391

Fix API::Namespaces routing to accept namepaces with dots

See merge request gitlab-org/gitlab-ce!22912

Fix Red/Orange data link markdown

See merge request gitlab-org/gitlab-ce!23461

Resolve "Status Emoji currently replaces avatar on mobile"

Closes #51029

See merge request gitlab-org/gitlab-ce!23408

Remove broken link and fix markdown formatting

See merge request gitlab-org/gitlab-ce!23467

Improve wording on disabling impersonation in api/README

See merge request gitlab-org/gitlab-ce!23472

Externalize strings from `/app/views/invites`

See merge request gitlab-org/gitlab-ce!23205

Move drop_site_statistics to be a post deployment migration

See merge request gitlab-org/gitlab-ce!23455

Upgraded Codesandbox packages

Closes #51210

See merge request gitlab-org/gitlab-ce!23475

ci/config: generalize Config validation into Gitlab::Config:: module

See merge request gitlab-org/gitlab-ce!23443

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/51210

Fix typo in method name "silence_stderr"

See merge request gitlab-org/gitlab-ce!23468

Remove auto deactivation when failed to create a pipeline via pipeline schedules

Closes #41231

See merge request gitlab-org/gitlab-ce!22243