Investigate sending all comms to the user via `gl_console_messages`

Currently, we inform the user of broadcast messages and for a Geo cluster, if the secondary has replication lag in different parts of the gitlab, gitlab-shell & gitaly codebases.

If would be great to have a single place where all commms bound for the user is located.

Context:

• !287 (comment 157454949)
• https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/26692#note_157453054
• #183 (closed)
• https://gitlab.com/gitlab-org/gitlab-ee/issues/9195