Release the focus or the site hold

Idempotent: releasing the caller's own released focus is 200 with the record. From the commit every reservation of this focus is inert; the alarm markers are then cleared in chunks. A claim the focuser holds on one of those alarms is not touched. A focus_id that is not the caller's is 409 focus_changed. A generation of the caller's that is no longer inside their CURRENT scope (a revoked grant, a camera that moved) is still released, but the answer is 409 focus_changed with their in-scope current focus or null: its scope is never returned. For a site hold id the body may be {"reason": "submit" | "flag_off"} (default submit); the hold's markers are cleared, its alarms return to the shared queue with their original queued_at, and a hold that is not the caller's is 409 hold_changed.