Add a service to proxy calls to Prometheus API

See merge request gitlab-org/gitlab-ce!26840

- Also refactor the get and json_api_get methods so that the get method
can be reused by the new proxy method.
- The new proxy method makes no changes to the request to the prometheus
server and response from the prometheus server. This allows it to be
used as a proxy to the Prometheus server, hence the name.

Quarantine failing tests

See merge request gitlab-org/gitlab-ce!27036

Remove EE-specific parts from FilteredSearchManager (CE-backport)

See merge request gitlab-org/gitlab-ce!27016

(cherry picked from commit a4d0b2435ff132da9bb238fea95672a6ddfd084d)

Fix IDE file dropdown

Closes #60021

See merge request gitlab-org/gitlab-ce!27015

Fix old image diff swipe view

Closes #56762

See merge request gitlab-org/gitlab-ce!26968

CE Backport: Re-use MR tabs styles to Epic tabs

See merge request gitlab-org/gitlab-ce!26935

IDE fix MR detection from fork

See merge request gitlab-org/gitlab-ce!26986

**Why?**
Currently the IDE loads a merge request based on only the
`source_branch` name. This means it loads MR's from
forks that have the same branch name (not good).

- This required updating the BE API to accept `source_project_id`

Show error when namespace/svc account missing

Closes #54506

See merge request gitlab-org/gitlab-ce!26362

Fixing single string values in the 'include:' keyword of gitlab-ci.yml validations

See merge request gitlab-org/gitlab-ce!26998

This fix is a followup to !24098 which introduced a validation of the
`include:` keyword of a gitlab-ci configuration file when triggered
from /ci/lint API calls.

However, there was a test case missing: the case of a single string as
value. I have added a test case for that which shows that the code was
not validating it correctly.

This commit fixes that to allow all `include:` valid inputs.

Fix capitalization of a sentence in CONTRIBUTING.md

See merge request gitlab-org/gitlab-ce!27021

Backport Resizable container component for gl-charts

See merge request gitlab-org/gitlab-ce!26843

* Fix up graph resize logic if navbar is collapsed

Add snapshot

Clarify the Runner registration and authentication tokens

See merge request gitlab-org/gitlab-ce!26996

Merge branch '9217-warn-on-git-fetch-over-ssh-if-the-secondary-is-lagging-the-primary' into 'master'

Display console messages, if available

See merge request gitlab-org/gitlab-ce!26692

Resolve "Hide Kubernetes cluster warning if project has cluster related"

See merge request gitlab-org/gitlab-ce!26749

Fix and expand Gitaly FindCommit caching

See merge request gitlab-org/gitlab-ce!27018

Fix UI anchor links after docs refactor

See merge request gitlab-org/gitlab-ce!26890

Display cluster form validation error messages inline

Closes #57602

See merge request gitlab-org/gitlab-ce!26502

Replace comment by variable

See merge request gitlab-org/gitlab-ce!27007

Instead of having a comment describing what a specific value is,
better to have a variable with a meaningful name.

https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/26248 added
support for deduplicating FindCommit requests using Gitaly ref name
caching. However, not all endpoints were covered, and in one case the
Gitaly wrapper wasn't actually surrounding the serialization step. We
can safely cache ref names between FindCommit calls for #index and #show
endpoints for merge requests and pipelines. This can significantly
reduce the number of FindCommit requests.

Improve the Review Apps documentation by using gitlab-rails console

See merge request gitlab-org/gitlab-ce!27006

**Why?**

Previously it managed this as an internal data property, but there
was extra complexity involved because the component doesn't have
all the information it needs (i.e. the `mouseOver` prop).

This is a good opportunity to colocate the data prop with the component
that has the information to change it (i.e. `file_row`) and let
`new_dropdown/index` receive this value as a prop.

Update gitlab/eslint-config version

See merge request gitlab-org/gitlab-ce!27008

Drop legacy artifacts usage as there are no leftovers

See merge request gitlab-org/gitlab-ce!24294

Fix a KeyError in GitlabSchema

Closes #60057

See merge request gitlab-org/gitlab-ce!27011

Rename Workhorse terminal_specification to channel_specification

See merge request gitlab-org/gitlab-ce!26939