This extends the dendrite monolith for pinecone to integrate the s&f
features into the mobile apps.
Also makes a few tweaks to federation queueing/statistics to make some
edge cases more robust.
This adds store & forward relays into dendrite for p2p.
A few things have changed:
- new relay api serves new http endpoints for s&f federation
- updated outbound federation queueing which will attempt to forward
using s&f if appropriate
- database entries to track s&f relays for other nodes
