[avalanche] Rationalize the local proof status in getavalancheinfo

Summary:
The getavalancheinfo RPC returns several info about the local proof, including a verified flag, a verification_status and a sharing flag.
This information has proven to be confusing, as the sharing flag doesn't give any information about why the proof is not shared, and one of the verification status is pending which doesn't indicate why the verification is pending.

This diffs deprecates the sharing flag in favor of a better verification status, so pending can be either pending verification or pending inbound connections which is equivalent to the previous sharing: false field.

Depends on D14565.

Test Plan:

ninja all check-all

Reviewers: #bitcoin_abc, PiRK

Reviewed By: #bitcoin_abc, PiRK

Differential Revision: https://reviews.bitcoinabc.org/D14566