This prevents some of the abusive behaviors, of someone putting 100000 and creating out of memory condition easily

Also corrects capitalisation of Git.

This allows users to add patches as attachments to merge request
created via email.

When an email to create a merge request is sent, all the attachments
ending in `.patch` will be applied to the branch specified in the
subject of the email. If the branch did not exist, it will be created
from the HEAD of the repository.

When the patches could not be applied, the error message will be
replied to the user.

The patches can have a maximum combined size of 2MB for now.

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

The private commit email is automatically generated in the format:
id-username@noreply.HOSTNAME

GitLab instance admins are able to change the HOSTNAME portion,
that defaults to Gitlab's hostname, to whatever they prefer.

Now the files are identical again compared to EE.

These are backported from
https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/5050

The container registry requires the `auth` config to be set up properly
or users will be able to download images that they are not authorized to
do so.

For example https://gitlab.com/gitlab-org/gitlab-runner/issues/3652

Label CI/CD has been deprecated (cf. ~CI/CD-DoNotUse ) and its description says to use ~Release or ~Verify

Also:

- Ensures documentation section adheres to linters.
- Makes other minor improvements.