Improve merge error when pre-receive hooks fail in fast-forward merge

See merge request gitlab-org/gitlab!44843

When fast-forward merge is enabled, merges might fail due to a failed
pre-receive check (e.g. due to file locks, commit message push rules,
etc.) but the UI would only display:

```
Merge failed: pre-receive hook failed. Please try again.
```

While the raw message was logged in Sentry and in `exceptions_json.log`,
this kept users in the dark.

Gitaly prefaces the error response status from the `/internal/allowed`
API call with `GitLab:`, so we can use this to display the error to the
user. We now only fallback to a default if we do not have anything to
show. Now, users see a more informative message, such as:

```
Merge failed: Commit message does not follow the pattern
'MERGEME'. Please try again.
```

Relates to https://gitlab.com/gitlab-org/gitlab/-/issues/246816

Finish Moving Feature Flags to Core RUN AS-IF-FOSS

See merge request gitlab-org/gitlab!44642

Update feature flags documentation
Finish moving feature flags to core

Upgrades all the buttons in the admin dir

See merge request gitlab-org/gitlab!44991

Change links to markdownlint and Vale versions

See merge request gitlab-org/gitlab!45031

Docs: Add links to install methods page

See merge request gitlab-org/gitlab!45030

Project settings: Replace fa-chevron-down with SVG

See merge request gitlab-org/gitlab!45021

Add close button to issue, MR and epic sidebar labels

See merge request gitlab-org/gitlab!42703

Clicking on this button removes the label, and was added
to improve the UX of label removal.

Adds status to jobs, stages, and groups

See merge request gitlab-org/gitlab!43069

* Adds the specs
* Adds schema and docs

Support flexible rollout strategy in the UX

See merge request gitlab-org/gitlab!43611

Include child pipeline builds in latest successful builds for ref/sha

See merge request gitlab-org/gitlab!29710

When looking for the latest successful build for a given ref or sha
we are now able to find builds created in child pipelines or child
of child pipelines.

Merge branch '215697-allow-groups-to-disable-2fa-requirement-for-subgroups-validations' into 'master'

Allow groups to disable 2FA requirement for subgroups - validations

See merge request gitlab-org/gitlab!44038

Add specs for new validation

Add validation in group

Add specs for new requires_two_factor_validation

WIP

Update validations for namespace setting

Update to Rack v2.1.4

See merge request gitlab-org/gitlab!44518

Allow placeholder `:id` for group link route

See merge request gitlab-org/gitlab!44346

Allows us to pass route with placeholder to frontend

Update integration descriptions to not be project-specific

See merge request gitlab-org/gitlab!44893

To not be project-specific.
- Make sure translations are updated as well.

Add note about cross site cookies browser limitation to Jira App page

See merge request gitlab-org/gitlab!44898

Remove duplicated BS display property from Commit/Snippet's HAML

See merge request gitlab-org/gitlab!44917

Use scan information in issue template

See merge request gitlab-org/gitlab!44620

Merge branch '235603-convert-group-members-list-view-from-haml-to-vue-role-dropdown-component' into 'master'

Group members Vue conversion - role dropdown

See merge request gitlab-org/gitlab!44651

Part of a larger initiative to convert the group members table from
HAML to Vue

This is needed to address a few outstanding CVEs and fix cookie
timestamp formats.

Full list of changes:
https://github.com/rack/rack/compare/2.0.9..2.1.4

Relates to:
* https://gitlab.com/gitlab-org/gitlab/-/issues/36362
* https://gitlab.com/gitlab-org/gitlab/-/issues/228622

Rack v2.1.x no longer coerces the body to a string. Previously in a few
places the Grape API was returning the status code as an integer, which
Grape used as the response body. To preserve the legacy behavior, we
explicitly set the body to the stringified integer.

Add status emoji to member avatar

See merge request gitlab-org/gitlab!44064

Part of a larger initiative to convert the group members view from
HAML to Vue

Fix params not filtered on project approval API

See merge request gitlab-org/gitlab!44885

Docs: Git rebase, force-push, merge conflicts

See merge request gitlab-org/gitlab!43887

Update metadata for SSH page

See merge request gitlab-org/gitlab!44322

Resolve "snowplow - count creating incidents via create incident button"

See merge request gitlab-org/gitlab!44631

Merge branch 'Replace-GlDeprecatedDropdown-with-GlDropdown-in-app/assets/javascripts/vue_shared/components/split_button.vue' into 'master'

Replace gl deprecated dropdown with gl dropdown in app/assets/javascripts/vue shared/components/split button.vue

See merge request gitlab-org/gitlab!41433