Implement tootctl accounts prune

[tribela]

Like tootctl statuses remove, This command will delete any remote account that is never interacted with local.
It removes many avatar/header images.

[ClearlyClaire]

Might be worth checking for reports as well, especially in case a status has been soft-deleted.

[tribela]

Thank you for reviewing this code. I'll work on it later today

[ClearlyClaire]

Looks good to me!

[tribela]

Should I add where(silenced_at: nil).where(suspended_at: nil)?

[weex]

I tried this out and found results to be modest. Wondering how it can be made more aggressive.

2219/2219 |=======================================| Time: 00:23:34
OK, pruned 2196 accounts

Before (from tootctl media usage):

Avatars:	5.65 GB (3.05 MB local)
Headers:	12.2 GB (2.04 MB local)

After

Avatars:	5.5 GB (3.05 MB local)
Headers:	11.9 GB (2.04 MB local)

[github-actions]

This pull request has merge conflicts that must be resolved before it can be merged.