We were looking these up on each request to an issue page, because the form is
pre-filled, as is the template dropdown. That was unnecessary: we could just
treat these as 'special' repository files (like the rendered README) and cache
them in Redis until they change on a push.

Replaces all the explicit include metadata syntax in the specs (tag:
true) into the implicit one (:tag).
Added a cop to prevent future errors and handle autocorrection.

`Repository#has_visible_content?` used to rely on the cached count of local branches, but
since it is now an independently cached value it needs to be invalidated on its own.

Closes #38646

When calling pre-receive, post-receive, and update hooks, add the GitLab
username as the GL_USERNAME environment variable.

This patch only handles cases where pushes are over http, or via
the web interface.  Later, we will address the ssh case.

Closes gitaly#601

Closes gitaly#562

So it's more clear what could happen. Also add
more tests about the behaviour.

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

Closes gitaly#443

Closes gitaly#433

Remove superfluous lib: true, type: redis, service: true, models: true, services: true, no_db: true, api: true

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