- 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>

The /licenses, /gitignores and /gitlab_ci_ymls endpoints are now also
available under a new /templates namespace. Old endpoints will be
deprecated when GitLab 9.0.0 is released.

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

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

  - Includes documentation and tests

Use NotificationSetting::EMAIL_EVENTS for params