Adding KRaft Monitoring Related Metrics to docs/ops.html

[niket-goel]

This commit adds KRaft monitoring related metrics to the Kafka docs (docs/ops.html).

All metrics contained in the following classes have been added to the commit:

BrokerServerMetrics
QuorumControllerMetrics
KafkaRaftMetrics

KRaft related KIPs mention more metrics, but this commit only adds in the metrics available in the source code at the time of authoring.