Feature: MSC2815 Support

[FSG-Cat]

Add a command that lets Draupnir with the use of MSC2815 ask for the pre redaction copy of a event. Yes this feature requires homeserver support but tbh a lot of our userbase has this enabled based on talking with other homeserver admins and moderators. Notable users who are notorious enough that i can reveal this capability being used is envs.net who uses it for their lounge room. The lounge room is a generic chit chat room.

The command syntax could be !draupnir show EVENT_ID or show_redacted EVENT_ID.

This feature works for AS and for Regular Draupnir but Regular Draupnir when its a Synapse Admin can use this feature in ANY room on servers with the feature enabled. The reason i would say we dont want to gatekeep this is due to that homeserver admins have legitimate reasons to use this API even in rooms they arent admin in. Further discussion on this might be desirable.

Should note that this is a P1 for people who have special clients configured that has this feature it could be argued or a P2 or even P3 for those who do not.