This changeset configures the RPC rate metrics that were added in #15515 to all
the RPCs that support authenticated HTTP API requests. These endpoints already
configured with pre-forwarding authentication in #15870, and a handful of others
were done already as part of the proof-of-concept work. So this changeset is
entirely copy-and-pasting one method call into a whole mess of handlers.
Upcoming PRs will wire up pre-forwarding auth and rate metrics for the remaining
set of RPCs that have no API consumers or aren't authenticated, in smaller
chunks that can be more thoughtfully reviewed.
