add delete-rooms admin command

[donjuanplatinum]

This subcommand delete-rooms can delete rooms by rooms index like
!admin rooms delete-rooms 1 2 3 --page 1

[donjuanplatinum]

It looks like an unnecessary trailing comma in src/core/utils/two_phase_counter.rs at the line 142
debug_assert!(self.check_pending(id), "sequence number must be currently pending",);
call triggered a CI failure in Clippy. I've removed it in the latest commit.

[jevolk]

It's probably a new nightly lint and you don't have to worry about it, thank you though 🙏🏻