[avalanche] Vote on transactions

Summary:
Currently guarded behind a hidden flag as the feature is far from complete.
Only voting is implemented, no polling occurs.

Test Plan:

./test/functional/test_runner.py abc_p2p_avalanche_transaction_voting

Reviewers: #bitcoin_abc, sdulfari

Reviewed By: #bitcoin_abc, sdulfari

Subscribers: sdulfari

Differential Revision: https://reviews.bitcoinabc.org/D12969