KAFKA-13965: Document broker-side socket-server-metrics

[abhi-ksolves]

Documented all the socket-server-metrics

Ticket Description -
There are a bunch of broker JMX metrics in the "socket-server-metrics" space that are not documented on kafka.apache.org/documentation
MBean: kafka.server:type=socket-server-metrics,listener=,networkProcessor=
From KIP-188: https://cwiki.apache.org/confluence/display/KAFKA/KIP-188+-+Add+new+metrics+to+support+health+checks
kafka.server:type=socket-server-metrics,name=connection-accept-rate,listener={listenerName}
From KIP-612: https://cwiki.apache.org/confluence/display/KAFKA/KIP-612%3A+Ability+to+Limit+Connection+Creation+Rate+on+Brokers

[github-actions]

A label of 'needs-attention' was automatically added to this PR in order to raise the
attention of the committers. Once this issue has been triaged, the triage label
should be removed to prevent this automation from happening again.