rpc: verify that circuit breakers actually fail fast on dial

[erikgrinaker]

This comment seems to indicate that we don't actually enable the circuit breaker for dials, which would be surprising and bad. But the reference to getBreaker() is stale so it may just be an outdated comment. We should find out, and either fix the comment or revisit the breakers.

cockroach/pkg/rpc/peer.go

Lines 63 to 66 in 8e02a8a

	// NB: at the time of writing, we don't use the breaking capabilities,
	// i.e. we don't check the circuit breaker in `Connect`. We will do that
	// once the circuit breaker is mature, and then retire the breakers
	// returned by Context.getBreaker.

Jira issue: CRDB-31501

[blathers-crl]

cc @cockroachdb/replication