[BE] Federation tests replication round1 - demonstrate absent replication of comment deletes #3657

This is an urgent test addition to highlight the problem with comment deletes not replicating when a remote-server creates the comment, the home server has no code to replicate delete of comment to all the downstream subscribe servers. Gamma serves as an example of the downstream servers subscribed who are not getting the delete in 0.18.2 version.

The intention here is to put more developer eyes on https://github.com/LemmyNet/lemmy/issues/3625