Fix broken documentation links

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/15249

- [x] `/help/ui`- This is working for me
- [x] `/help/ci/examples/deployment/README.md` - Fixed
- [x] `/help/ci/api/projects.md` - Fixed
- [x] `/help/markdown/LICENSE` - Cannot do much to fix it, added a note.
- [x] `/help/ci/ssh/README.md` - Cannot find this link referenced anywhere.

See merge request !3903

Fixed advice on invalid permissions on upload path

When running the checks, my upload path has wrong permissions, the advice could not fix it because it does not change the permission of this directory (only sub-directories).
```
Uploads directory setup correctly? ... no
  Try fixing it:
  sudo find /home/git/gitlab/public/uploads -type d -not -path /home/git/gitlab/public/uploads -exec chmod 0700 {} \;
  For more information see:
  doc/install/installation.md in section "GitLab"
  Please fix the error above and rerun the checks.
```

Executing this instead fixed the error :
```
sudo chmod 700 /home/git/gitlab/public/uploads
```

See merge request !2948

Added helper methods for database migrations

These helpers can ultimately be used to write migrations that don't
require downtime.

See #15464 for more information.

See merge request !3860

Fix warning messages with SVG ALLOWED_ELEMENTS

Define the right module names so that Rails autoloading and eager loading will work properly.

Eliminates "warning: already initialized constant Gitlab::Sanitizers::SVG::ALLOWED_ELEMENTS"

See merge request !4207

Changing the confidentiality of an issue now creates a new system note

Closes #15236.

See merge request !4189

Revert "Merge branch 'issues/15127' into 'master'"

This reverts merge request !3647


See merge request !4212

This reverts merge request !3647

Eliminates "warning: already initialized constant Gitlab::Sanitizers::SVG::ALLOWED_ELEMENTS"

fix #15127 ActiveJob::DeserializationError thrown

`send_devise_notification` pre-maturely enqueued the task when the user instance
has not yet been committed into the database, causing a record-not-found in the
other sidekiq process.

`devise-async` has already been taking care of asynchronous mail sending, we just
need to run it inside queue `mailers` instead of `mailer` to enable it.

The implementation of `devise-async` enqueues the task in `after_commit` hook
which is the right way to do it.

See merge request !3647

Mask credentials from URL when the import of project has failed.

REF: #17560 

See merge request !4185

Remove unused Project scopes

Closes #17635.

See merge request !4204

Signed-off-by: Rémy Coutable <remy@rymai.me>

Fix changelog for 7.9.3

Closes #1484 

See merge request !4202

Signed-off-by: Rémy Coutable <remy@rymai.me>

fix example urls for (dis)associating runners to projects



See merge request !2993

doc: fix git lfs workaround for using http instead of https

the url should only point to `info/lfs` instead of `info/lfs/batch/objects`

See merge request !2713

Remove User#tm_in_authorized_projects and User#tm_of

These methods seems to be unused.

Closes #17628.
Signed-off-by: Rémy Coutable <remy@rymai.me>

See merge request !4198

Remove back-compat code that's not needed anymore

Solves #15584.

See merge request !4187

These methods seems to be unused.
Signed-off-by: Rémy Coutable <remy@rymai.me>

Add container registry support

Tasks:

- [x] Merge docker/distribution authentication service: https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/3787
- [x] Implement Docker Registry API
- [x] Show a list of docker images in GitLab
- [x] Remove registry repository on project deletion
- [x] Support project rename, move and namespace rename
- [x] Use token when connecting the registry
- [x] Allow to delete images from GitLab
- [x] Support pushing from GitLab CI (gitlab-ci-token / $CI_BUILD_TOKEN)
- [x] Support GitLab Runner pulling for public repositories
- [ ] Support GitLab Runner pulling for private repositories
- [x] Add tests for Docker Registry API
- [x] Add tests for a views
- [x] Make texts nicer
- [x] Implement a backup support

- [ ] Create administration documentation https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/4141
- [ ] Create user documentation

See merge request !4040

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

Fix atom feeds and links

1. The atom feed for a group's issues didn't work, because it had parts copied from the dashboard issues builder template.
2. The feed link from a group's activity page went to the dashboard feed, rather than the group's feed.

Closes #15640

See merge request !4191

Fix broken link in CI quickstart docs

The newline between the `[label]` and the `(link)` caused it to be interpreted literally: http://doc.gitlab.com/ce/ci/quick_start/README.html

See merge request !3541

Improve issue formatting in Slack service

This will improve the looks of the message that gets send to Slack.

**Before**

![image](https://gitlab.com/jeroenvanbaarsen/gitlab-ce/uploads/670442d4d5cef5aa36753671b8894a75/image.png)

**After**

![image](https://gitlab.com/jeroenvanbaarsen/gitlab-ce/uploads/ab6e40a0c22ebe89ebd5b3652821c6dd/image.png)

There is one thing I'm not certain about, thats sending the logo with the payload. Because this means we need to host the GitLab logo somewhere public, and every time a payload from any GitLab instance is send, we use that logo url. This might overload the server, or drive the bandwidth bill through the roof.
This is something @sytses or @dzaporozhets have to decide about.

@stanhu, you told me you were the author of the original code, maybe you can review?

See merge request !1308

Fixed typo in zen.scss and corresponding views



See merge request !4045

Make it clearer that /licenses is the OS license templates endpoint

Following the discussion on https://gitlab.com/gitlab-org/gitlab-ce/commit/13804aba867d19009ca94d820aa7ec650a509f5a#note_4961954.

Corresponding EE MR: https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/407

See merge request !4188

Signed-off-by: Jeroen van Baarsen <jeroenvanbaarsen@gmail.com>