Enables frozen string for some vestigial files as
well as the following:

* app/controllers/projects/**/*.rb
* app/controllers/sherlock/**/*.rb
* app/controllers/snippets/**/*.rb
* app/controllers/users/**/*.rb

Partially addresses #47424.

The status is shown for
- The author of a commit when viewing a commit
- Notes on a commit (regular/diff)
- The user that triggered a pipeline when viewing a pipeline
- The author of a merge request when viewing a merge request
- The author of notes on a merge request (regular/diff)
- The author of an issue when viewing an issue
- The author of notes on an issue
- The author of a snippet when viewing a snippet
- The author of notes on a snippet
- A user's profile page
- The list of members of a group/user

This refactors the Markdown pipeline so it supports the rendering of
multiple documents that may belong to different projects. An example of
where this happens is when displaying the event feed of a group. In this
case we retrieve events for all projects in the group. Previously we
would group events per project and render these chunks separately, but
this would result in many SQL queries being executed. By extending the
Markdown pipeline to support this out of the box we can drastically
reduce the number of SQL queries.

To achieve this we introduce a new object to the pipeline:
Banzai::RenderContext. This object simply wraps two other objects: an
optional Project instance, and an optional User instance. On its own
this wouldn't be very helpful, but a RenderContext can also be used to
associate HTML documents with specific Project instances. This work is
done in Banzai::ObjectRenderer and allows us to reuse as many queries
(and results) as possible.

This ensures that we have more visibility in the number of SQL queries
that are executed in web requests. The current threshold is hardcoded to
100 as we will rarely (maybe once or twice) change it.

In production and development we use Sentry if enabled, in the test
environment we raise an error. This feature is also only enabled in
production/staging when running on GitLab.com as it's not very useful to
other users.

I've followed the [upgrade guide](https://github.com/thoughtbot/factory_bot/blob/4-9-0-stable/UPGRADE_FROM_FACTORY_GIRL.md) and ran these two commands:

```
grep -e FactoryGirl **/*.rake **/*.rb -s -l | xargs sed -i "" "s|FactoryGirl|FactoryBot|"
grep -e factory_girl **/*.rake **/*.rb -s -l | xargs sed -i "" "s|factory_girl|factory_bot|"
```

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

Adds a rubocop rule (with autocorrect) to ensure line break after guard clauses.