Adding possibility to delete messages after sync

[kopiro]

As stated, adding delete_messages = 0 | 1 | 2 option to allow messages deletion after sync.

[knadh]

Thanks for the PR @kopiro. I think this is best done with a commandline flag. Of thousands, if not tens of thousands of messages that are fetched and stored in the DB, only a few would typically need to be deleted by hand. And this is a one-off action. So adding that to the permanent configuration isn't ideal.

Something like tg-archive maintain --delete=1,2,3,4,5 would be ideal. A new "maintain" mode like "sync" with a flag to take arbitrary message IDs which are directly deleted from the DB.