[grouping] Consider storing metadata on `GroupHash` records

[lobsterkatie]

It's come up a couple times that it'd be great to have more information about how a particular GroupHash record came to be and/or came to be in its current state.

• Grouping config version (would have to decide if it's first version to calculate that hash value or latest version)
• If Seer is involved, the fact that the hash is represented in the Seer DB, Seer model version, parent hash (if any) - useful for display in the Grouping Info section of the issue details page, and for debugging the grouping of a given event.
• If the issue's been merged, maybe the id the Activity record of the merge so we can get more data from that if desired
• Possibly the grouping enhancements currently stored on each event (so that they don't have to be), maybe along with a dump of the stacktrace which was enhanced, and/or the full grouping info variants data (so we can know which hashes come from message vs stacktrace vs whatever)
• Other things?

[lobsterkatie]

This is running in prod now. Closing this.