release-21.1: sql/pgwire: add ops logging for draining events

[mikeCRL]

Michael Lewis (mikeCRL) commented:

PR: https://github.com/cockroachdb/cockroach/pull/66874

From release notes:

Added logs for important events during the server draining/shutdown process: (1) log when the server closes an existing connection while draining, (2) log when the server rejects a new connection while draining, and (3) log when the server cancels in-flight queries after waiting for the [server.shutdown.query_wait](../v21.1/cluster-settings.html] duration to elapse while draining. [#66874][#66874) {% comment %}doc{% endcomment %}

Jira Issue: DOC-1450