[YSQL] Clarify active queries endpoint

Jira Link: DB-9881

Description

The output at :13000/rpcz is called Live Ops in the :9000/utilz page. This can be misleading because the output includes all live backends, whether or not they are currently running.

e.g.

{
    "connections": [
        {
            "db_oid": 13248,
            "db_name": "yugabyte",
            "query": "select pg_size_pretty(pg_table_size('t'::regclass));",
            "process_start_time": "2024-02-01 11:36:46.388855-08",
            "query_start_time": "2024-02-01 11:37:01.953452-08",
            "application_name": "ysqlsh",
            "backend_type": "client backend",
            "backend_status": "idle",
            "host": "127.0.0.1",
            "port": "60681"
        },
        {
            "process_start_time": "2024-01-31 13:42:49.356584-08",
            "application_name": "",
            "backend_type": "checkpointer",
            "backend_status": ""
        }
    ]
}

Shows an idle backend and its last run query. At first glance it might look like this query is still running.

Issue Type

kind/enhancement

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