Collect and present additional ProxySQL metrics taken from `runtime_mysql_servers` table

It's required to review a community PR about adding collector from runtime_mysql_servers table.

User impact:
Now we are collecting statuses from stats_mysql_connection_pool table.
But according to discussion sysown/proxysql#1817
stats_mysql_connection_pool collects way more statistics than just the status of the server: it reports number of current connections and historical one (successful and not), number of queries, and bytes sent/received.
Therefore when a server is removed, it isn't immediately deleted from stats_mysql_connection_pool, or these statistics are lost.
So such data can't be used in alerts.

Also it's required to add "Endpoint Details Status" element on "ProxySQL Instance Summary" dashboard.  Data is provided by the new collector.