Create an insight or event for poor connection health or activity (e.g., long-running idle sessions)

It's difficult to identify idle sessions/connections that are problematic causing downstream issues such as contention. We should surface an insight or event that highlights this behavior so users can further investigate the underlying issue and take the appropriate mitigation steps (e.g., manually cancel the session, reconfigure connection pool, evaluate network health, etc.).

Jira issue: CRDB-35954