[avalanche] Manage proof reception

Summary:
Upon proof reception, we should create a peer (no associated node yet),
relay the proof and update the tracker status.

Depends on D9660.

Ref T1611.

Test Plan:
With Clang and debug:

ninja all check-all

Reviewers: #bitcoin_abc, PiRK

Reviewed By: #bitcoin_abc, PiRK

Maniphest Tasks: T1611

Differential Revision: https://reviews.bitcoinabc.org/D9662