[avalanche] Add a way to check if a proof is a remote proof

Summary: Stake contender preconsensus will need a way to check if a proof is a remote proof. GetStakeContenderStatus() could be used but this is much more lightweight.

Test Plan:

ninja check-avalanche-peermanager_tests

Reviewers: O1 Bitcoin ABC, #bitcoin_abc, Fabien

Reviewed By: O1 Bitcoin ABC, #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D16932