basically relays send us a lot of announce activities to share posts
but we don't care about those activities: it's db bloat and it increases
the shares count. keep a table keeping track of followed relays and
lazily skip activities by them, just fetch. IMPORTANT relays are only
loaded at startup, so if you subscribe to a new relay restart your
server once it accepts!!!
remote activities for Likes and Follows should still be added to our
database so we know where to verify those and we can present them in a
timeline for notifications