only retrieve pubkey once for all validators (partially fixes #4865) (#4895)

in consensus/state.go, when calulating metrics, retrieve address (ergo, pubkey) once prior to iterating over validatorset to ensure we do not make excessive calls to signer.

Partially closes: #4865

CHANGELOG_PENDING.md

@@ -21,3 +21,4 @@ program](https://hackerone.com/tendermint).
 
 ### BUG FIXES:
 
+- [consensus] [\#4895](https://github.com/tendermint/tendermint/pull/4895) Cache the address of the validator to reduce querying a remote KMS (@joe-bowman)

consensus/state.go

@@ -1463,7 +1463,13 @@ func (cs *ConsensusState) recordMetrics(height int64, block *types.Block) {
 	var (
 		missingValidators      = 0
 		missingValidatorsPower int64
+		address                types.Address
 	)
+
+	if cs.privValidator != nil {
+		address = cs.privValidator.GetPubKey().Address()
+	}
+
 	for i, val := range cs.Validators.Validators {
 		var vote *types.CommitSig
 		if i < len(block.LastCommit.Precommits) {
@@ -1474,7 +1480,7 @@ func (cs *ConsensusState) recordMetrics(height int64, block *types.Block) {
 			missingValidatorsPower += val.VotingPower
 		}
 
-		if cs.privValidator != nil && bytes.Equal(val.Address, cs.privValidator.GetPubKey().Address()) {
+		if bytes.Equal(val.Address, address) {
 			label := []string{
 				"validator_address", val.Address.String(),
 			}