[avalanche] Save the remote proofs from our avalanche outbound peers

Summary:
And add a RPC to retrieve them. So far only the present status can be set.

Depend on D14661.

Test Plan:

./test/functional/test_runner.py abc_p2p_avalanche_remote_proofs

Reviewers: #bitcoin_abc, PiRK, bytesofman

Reviewed By: #bitcoin_abc, PiRK, bytesofman

Subscribers: bytesofman

Differential Revision: https://reviews.bitcoinabc.org/D14662