[avalanche] Improve the getavalancheinfo RPC

Summary:
This RPC has been provably confusing during the tests, so let's try to make it better:

• Rename some fields:
  • active => ready_to_poll
  • live => verified
  • orphan_proof_count => immature_proof_count (needs to be updated in others places as well but out of scope)
• Include ourself in the total proof, node and stake count. This means that the total is now given directly with no math involved, and all the nodes from the network will get the same values as an RPC output.
• Improve the documentation to reflect these changes.

Test Plan:

./test/functional/test_runner.py abc_rpc_getavalancheinfo

Reviewers: #bitcoin_abc, sdulfari

Reviewed By: #bitcoin_abc, sdulfari

Differential Revision: https://reviews.bitcoinabc.org/D11857