[avalanche] Send avalanche proofs upon request

Summary:
This makes the node answer the proof inv requests from a getdata
message. To prevent fingerprinting the following conditions must be met:

• the inv should have been recently announced, or
• the proof is known (has been added) for more than 2 minutes

Depends on D9642 and D9643.

Ref T1611.

Test Plan:

ninja all check-all

Reviewers: #bitcoin_abc, PiRK

Reviewed By: #bitcoin_abc, PiRK

Maniphest Tasks: T1611

Differential Revision: https://reviews.bitcoinabc.org/D9644