`delete_previous!` deletes existing topics even when we cannot send a new one due to the `limit_once_per` option. The dashboard problems PM gets deleted the next time the job runs (30 minutes), so the inbox could be empty when
admins click on the summary notification.
We send the reminder using the GroupMessage class, which supports removing previous messages. We can't match them by raw because they could mention different moderators. Also, I had to change the subject to remove dynamically generated values, which is necessary for finding them.
Discourse is sending regularly message to admins when potential problems are persisted. Most of the time they have exactly the same content. In that case, when there are no replies, the old one should be trashed before a new one is created.
Zeitwerk simplifies working with dependencies in dev and makes it easier reloading class chains.
We no longer need to use Rails "require_dependency" anywhere and instead can just use standard
Ruby patterns to require files.
This is a far reaching change and we expect some followups here.
This reduces chances of errors where consumers of strings mutate inputs
and reduces memory usage of the app.
Test suite passes now, but there may be some stuff left, so we will run
a few sites on a branch prior to merging
