This commits allow to select merge train concurrency via
feature flag. The new parallel factor is disabled by default.

Added note about data driven tests

See merge request gitlab-org/gitlab!16882

Adds a section to the FE testing guidelines
about data driven jest tests.

Edits docs on disabling group/project notifications

Closes #30995

See merge request gitlab-org/gitlab!18980

Improve instance mirroring help text

Closes #13769

See merge request gitlab-org/gitlab!19047

A bug was reported with mirroring because it wasn't clear that both
push and pull mirroring are disabled by this option.

Improved help text and API docs should make this clearer for those
who chose to use this feature.

Merge branch 'pcalder-34956-spec-lib-gitlab-experimentation_spec-rb-77-broken-or-very-flaky-patch-17311' into 'master'

Temporarily bypass flaky experiment test

See merge request gitlab-org/gitlab!19134

Show timeframe dates for an epic in Epics list page

See merge request gitlab-org/gitlab!19006

Clarify changelog for flagged features with DB changes

See merge request gitlab-org/gitlab!19019

Remove expectation on alerts that may have disappeared already

Closes #34834

See merge request gitlab-org/gitlab!19091

Update feature tier for CI_JOB_TOKEN

See merge request gitlab-org/gitlab!18810

Fix grammar in i18n .po file details

See merge request gitlab-org/gitlab!17695

Fix project imports not working with serialized data

Closes #34860

See merge request gitlab-org/gitlab!19124

Edit job logs text

See merge request gitlab-org/gitlab!18770

Add a new entry for Sentry

See merge request gitlab-org/gitlab!19038

Set shorter TTL for all unauthenticated requests

See merge request gitlab-org/gitlab!19064

The change in e404c311 broke models that
relied on single-type inheritance:

```
CommitStatus.new(type: 'Ci::Build').class
=> Ci::Build

CommitStatus.new.tap{|c| c.assign_attributes(type: 'Ci::Build')}.class
=> CommitStatus
```

As a result, any serialized options would not be properly saved to the
database, leading to errors expecting a `Hash` vs. a `String`, for
example.

This affected all pipelines that used shared runners because the build
would error out due to this serialization error.

Closes https://gitlab.com/gitlab-org/gitlab/issues/34860

Allow adding requests to performance bar manually

See merge request gitlab-org/gitlab!18464

Fix N+1 for group container repositories view

See merge request gitlab-org/gitlab!18979

Disable a flaky frontend test

See merge request gitlab-org/gitlab!19096

Upgrade gitlab-ui once source code is move to src/ directory

See merge request gitlab-org/gitlab!18966

Enable frozen string for spec/policies

See merge request gitlab-org/gitlab!19073

Resolve "Remove pendo from GitLab-FOSS"

Closes #34852

See merge request gitlab-org/gitlab!19105

Check for enums not using smallint

Closes #25012

See merge request gitlab-org/gitlab!18179

Revert adding user id to snowplow

See merge request gitlab-org/gitlab!19109

Clean up duplicate indexes on ci_trigger_requests

Closes #34818

See merge request gitlab-org/gitlab!19053

Document docs.gitlab.com monthly release process

Closes gitlab-docs#245

See merge request gitlab-org/gitlab!16765

Mostly port content from the gitlab-docs project
and streamline the monthly release process.

Add back in password passthrough for QA user

Closes #34807

See merge request gitlab-org/gitlab!19039

Removed in error last week, without this tests can't pass through
a password for the user they want to use