Quota metric tags are inconsistent

When enabling metrics for quotas the metrics apply to all clients (see https://issues.apache.org/jira/browse/KAFKA-13742).

Though, the tags are calculated depending on the quotas registered and applied to all clients: https://github.com/apache/kafka/blob/0b9a8bac36f16b5397e9ec3a0441758e4b60a384/core/src/main/scala/kafka/server/ClientQuotaManager.scala#L649-L694

This causes different metric tags result depending on which quota is registered first.

For instance, if a quota is registered with userId and clientId, then metrics are tagged with both, though if then a quota is registered with only tagged with clientId, then all metrics are only tagged by clientId — even though user principal is available.

I managed to reproduce this behavior here:

• From 10:30 to 10:45, there was a quota with both client-id and user-id
• It was removed by 10:45, so no metrics were exposed.
• After, a quota with client id was created, and metrics were collected only with client id, even though the user was available.

I'd expect metrics to always contain both, if available — and simplify the logic here https://github.com/apache/kafka/blob/0b9a8bac36f16b5397e9ec3a0441758e4b60a384/core/src/main/scala/kafka/server/ClientQuotaManager.scala#L649-L694.