- To prevent an attacker from enumerating the `/users` API to get a list of all
  the admins.

- Display the `is_admin?` flag wherever we display the `private_token` - at the
  moment, there are two instances:

  - When an admin uses `sudo` to view the `/user` endpoint
  - When logging in using the `/session` endpoint

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

CE port of https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/962

Implement module for setting "Poll-Interval" response header.
Return 429 in ETag caching middleware when polling is disabled.

In APIv1 we've been sending all jobs from previous stages and
a `dependencies` list with names of jobs that user want to download
artifacts from. This was selected on Runners side.

In APIv1 we've planned to send only jobs that were defined (if any; and
all previous jobs by default). However I've missed the fact that
it was Runner who selected jobs, not GitLab. And now current version
of APIV4 sends all jobs everytime.

This commit fixes this. If user will define `dependencies` in his job,
then GitLab will send only selected jobs.

Artifacts download for authorization is using a job token of job to
which the artifact belongs. In APIv1 the token was sent with dependent
jobs details and in APIv4 it was designed to also contain it.

However I forgot about this parameter while working on
`/api/v4/jobs/request` endpoint.

This commit adds a missing parameter which is required for APIv4 to work
properly.

[ci skip]

This commit only renames the commits, the cascading effects will be
dealt with later.

Fixes gitlab-org/gitlab-ce#28515

[ci skip]

Add `visibility` & `visibility=` methods to the
`Gitlab::VisibilityLevel` module so the `visibility_level` can be
get/set with a string value.

Use strings for the ApplicationSetting properties:
 - restricted_visibility_levels
 - default_project_visibility
 - default_snippet_visibility
 - default_group_visibility

Instead of exposing the VisibilityLevel as Integer, expose it as
String `visibility`.

Instead of exposing the VisibilityLevel as Integer, expose it as
String `visibility` for Project and ProjectSnippet.

Filter queries also accept the `visibility` as String instead of
`visibility_level` as Integer.

Also remove the `public` boolean.

 Rename column in the database
 Rename fields related to import/export feature
 Rename API endpoints
 Rename documentation links
 Rename the rest of occurrences in the code
 Replace the images that contain the words "build succeeds" and docs referencing to them
 Make sure pipeline is green and nothing is missing.

updated doc images

renamed only_allow_merge_if_build_succeeds in projects and fixed references

more updates

fix some spec failures

fix rubocop offences

fix v3 api spec

fix MR  specs

fixed issues with partials

fix MR spec

fix alignment

add missing v3 to v4 doc

wip - refactor v3 endpoints

fix specs

fix a few typos

fix project specs

copy entities fully to V3

fix  entity error

more fixes

fix failing specs

fixed missing entities in V3 API

remove comment

updated code based on feedback

typo

fix spec

This reverts commit cb10b725c8929b8b4460f89c9d96c773af39ba6b.

Fixes #23895.

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