Our friends at GitHub show the programming languages for a long time,
and inspired by that this commit means to create about the same
functionality.

Language detection is done through Linguist, as before, where the
difference is that we cache the result in the database. Also, Gitaly can
incrementaly scan a repository. This is done through a shell out, which
creates overhead of about 3s each run. For now this won't be improved.

Scans are triggered by pushed to the default branch, usually `master`.
However, one exception to this rule the charts page. If we're requesting
this expensive data anyway, we just cache it in the database.

Edge cases where there is no repository, or its empty are caught in the
Repository model. This makes use of Redis caching, which is probably
already loaded.

The added model is called RepositoryLanguage, which will make it harder
if/when GitLab supports multiple repositories per project. However, for
now I think this shouldn't be a concern. Also, Language could be
confused with the i18n languages and felt like the current name was
suiteable too.

Design of the Project#Show page is done with help from @dimitrieh. This
change is not visible to the end user unless detections are done.

The Unicorn master resets any signal handlers and prevents rbtrace
from working properly as a result. Move the `require 'rbtrace'` call
to the Unicorn `after_fork` block and keep the initializer only for Sidekiq.

The previous implementation would hit the database each time
and provide a dummy response. If the database goes down, this
means all application workers would be taken out of service.
Simplify this check by using a Rails middleware that intercepts
this endpoint and returns a 200 response.

This reverts merge request !20679

This is mainly the setup of mutations for GraphQL. Including
authorization and basic return type-structure.

This will be enabled if ENABLE_RBTRACE environment variable is defined.
This will allow us to debug all sorts of issues in production:

https://github.com/tmm1/rbtrace

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

The removal in 4d376c66 had an unintended
side effect in that it got rid of the `require 'rouge/plugins/redcarpet'`.

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

For one README.md file, this instrumentation was adding several seconds and
significant RAM and CPU overhead since these filters often iterate through
all HTML nodes in tight loops.

Relates to #49409

This will enable bootsnap whenver the gem is available.

We also try to unify the way we setup OmniAuth, and how we check
if it's enabled or not.

By default, all sessions are given the same expiration time configured in the
session store (e.g. 1 week). However, unauthenticated users can generate a lot
of sessions, primarily for CSRF verification. It makes sense to reduce the TTL
for unauthenticated to something much lower than the default (e.g. 1 hour) to
limit Redis memory. In addition, Rails creates a new session after login,
so the short TTL doesn't even need to be extended.

Closes #48101