Refresh project authorizations using a Redis lease

This MR changes `User#refresh_authorized_projects` so it uses a Redis lease instead of relying on serializable transactions. See the commit message(s) for more details.

See merge request !7733

Expose coverage on GET pipelines/:id

Closes gitlab-org/gitlab-ce#24801

See merge request !7670

Fix: Timeout creating and viewing merge request for binary file

See merge request !7713

The coverage wasn't exposed yet, now it is but only for detailed
requests to save queries on the database.

Slash commands improvements

See merge request !7638

When I proposed using serializable transactions I was hoping we would be
able to refresh data of individual users concurrently. Unfortunately
upon closer inspection it was revealed this was not the case. This could
result in a lot of queries failing due to serialization errors,
overloading the database in the process (given enough workers trying to
update the target table).

To work around this we're now using a Redis lease that is cancelled upon
completion. This ensures we can update the data of different users
concurrently without overloading the database.

The code will try to obtain the lease until it succeeds, waiting at
least 1 second between retries. This is necessary as we may otherwise
end up _not_ updating the data which is not an option.

Resolve "Reduce queries in API::Helpers#find_project"

See merge request !7714

For example, now we support `/gitlab issue show #1`. Where the # used
to trip the regex.