Document "Maximum artifacts size" setting in Admin
The "Maximum artifacts size" setting is undocumented. This was introduced in https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/1584
This seems to be creating some confusion, see https://gitlab.com/gitlab-org/gitlab-ce/issues/14841#note_12001981
When searching for the error that occurs as a result of the maximum size limit
ERROR: Uploading artifacts to coordinator... too large archive id=94 responseStatus=413 Request Entity Too Large status=413 Request Entity Too Large token=
The most common results point to. The setting seems to be pointed out in each issue.
The setting should be documented to avoid future confusion.