- Declaring an endpoint's scopes in a `before` block has proved to be
  unreliable. For example, if we're accessing the `API::Users` endpoint - code
  in a `before` block in `API::API` wouldn't be able to see the scopes set in
  `API::Users` since the `API::API` `before` block runs first.

- This commit moves these declarations to the class level, since they don't need
  to change once set.

Restrict API X-Frame-Options to same origin

See merge request !2103

Ran:
 - git format-patch v9.2.2..v9.2.5 --stdout > patchfile.patch
 - git checkout -b 9-2-5-security-patch origin/v9.2.2
 - git apply patchfile.patch
 - git commit
 - [Got the sha ref for the commit]
 - git checkout -b upstream-9-2-security master
 - git cherry-pick <SHA of the patchfile commit>
 - [Resolved conflicts]
 - git cherry-pick --continue

Ran:
 - git format-patch v9.2.2..v9.2.5 --stdout > patchfile.patch
 - git checkout -b 9-2-5-security-patch origin/v9.2.2
 - git apply patchfile.patch
 - git commit
 - [Got the sha ref for the commit]
 - git checkout -b upstream-9-2-security master
 - git cherry-pick <SHA of the patchfile commit>
 - [Resolved conflicts]
 - git cherry-pick --continue

* Meld the following disparate endpoints:
 * `/projects/:id/events`
 * `/events`
 * `/users/:id/events`
+ Add result filtering to the above endpoints:
 * action
 * target_type
 * before and after dates

There was a race condition issue when the application was generating an
email and was using a language that was previously being used in other
request.

- As opposed to the issue `id` that was previously being used.
- This brings the API routes closer to the web interface's routes.
- This is specific to API v4.

Fixes gitlab-org/gitlab-ce#28515

[ci skip]

The `projects/:id/pipelines` exposed a lot of extra details
that are superfluous and it was taking extra resources to fetch them.

To get more details about a pipeline, use
`projects/:id/pipelines/:pipeline_id`.

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

  - Adds Registry events API endpoint
  - Adds container_images_repository and container_images models
  - Changes JWT authentication to allow multi-level scopes
  - Adds services for container image maintenance

Fixes #26051.
Signed-off-by: NRémy Coutable <remy@rymai.me>

- Move the `Oauth2::AccessTokenValidationService` class to
  `AccessTokenValidationService`, since it is now being used for
  personal access token validation as well.

- Each API endpoint declares the scopes it accepts (if any). Currently,
  the top level API module declares the `api` scope, and the `Users` API
  module declares the `read_user` scope (for GET requests).

- Move the `find_user_by_private_token` from the API `Helpers` module to
  the `APIGuard` module, to avoid littering `Helpers` with more
  auth-related methods to support `find_user_by_private_token`

Adding the necessary API for the new /snippets Restful resource
added with this commit. Added a new Grape class `Snippets`, as
well as a `PersonalSnippet` entity.

Issue: #20042
Merge-Request: !6373
Signed-off-by: NGuyzmo <guyzmo+gitlab+pub@m0g.net>