[avalanche] split the test suite into 2 suites

Summary:
The avalanche functional is getting complicated. This splits the
current test suite into 2 separate tests:

• fork resolution and voting
• proofs and node response to invalid proofs

This will hopefully reduce the conflicts and the need for rebasing while working on distinct aspects of the avalanche codebase.

Replaces D9350

Test Plan: ninja && test/functional/test_runner.py abc_p2p_a* abc_rpc_a*

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D9351