Add documentation about the log file `repocheck.log`
Description
Our documentation about logs (https://docs.gitlab.com/ce/administration/logs.html) does not include a log that the application creates, repocheck.log
.
The method that creates this log is https://gitlab.com/gitlab-org/gitlab-ee/blob/master/lib/gitlab/repository_check_logger.rb
Proposal
We should document this file in the rest of the documentation about logs.
cc @seanpackham