Rename inherited metrics cas_propose and cas_commit
to cas_accept and cas_learn respectively.
A while ago we made a decision to stick to widely accepted
terms for Paxos rounds: prepare, accept, learn. The rest
of the code is using these terms, so rename the metrics
to avoid confusion/technical debt.
While at it, rename a few internal methods and functions.
Fixes#6169
Message-Id: <20200414213537.129547-1-kostja@scylladb.com>
18b9bb57ac