Move the api resources section from the api readme
to it's own file, and adjust/link accordingly

PATs are accepted using the OAuth2 compliant header
"Authorization: Bearer {token}" in order to allow for
OAuth requests while 2FA is enabled.

Removing extra blank lines in docs that serve
no purpose, as well as some --- lines that also
are not needed.

Code blocks should not be spaced 4 times, as this will
prevent the code from being colored. They should
also be spaced the same as the lists they are a part
of, to make reading easier.

Previously, we used brackets to denote the tier badges,
but this made Kramdown, the docs site Markdown renderer,
show many warnings when building the site. This is now
fixed by using parentheses instead of square brackets.

This was caused by [PREMIUM] looking like a link to
Kramdown, which couldn't find a URL there.

See:
- https://gitlab.com/gitlab-com/gitlab-docs/merge_requests/484
- https://gitlab.com/gitlab-org/gitlab-ce/issues/63800

Adds the missing link to issues_statistics api endpoint

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

- Breaks up into more sections.
- Also minor fixes to pages within sections.

This includes a set of APIs to manipulate container registry.
This includes also an ability to delete tags based on requested
criteria, like keep-last-n, matching-name, older-than.

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

Project cluster API was included on 11.7. This MR describes the new
project cluster endpoints

Replace all '9koXpg98eAheJpvBs5tK' occurrences with
'<your_access_token>' in API docs.

- While here, restructure list slightly.

Adds gitlab.impersonation_enabled config option defaulting to true to
keep the current default behaviour.

Only the act of impersonation is modified, impersonation token
management is not affected.

This new endpoint allow users to update a submodule's reference.

The MR involves adding a new operation RPC operation in gitaly-proto
(see gitlab-org/gitaly-proto!233) and change Gitaly to use this
new version (see gitlab-org/gitaly!936).

See gitlab-org/gitlab-ce!20949