[Improvement] Provide Metrics for Gravitino MySQL Backend Storage Connect Pool

[TEOTEO520]

What would you like to be improved?

Currently, many parameters of the MySQL backend connection pool used by Gravitino, such as maxConnectCount and maxIdleConnect, are not configurable, and no relevant monitoring is configured for this connection pool. However, in reality, nearly every Gravitino REST request involves a call to the backend storage. Therefore, I believe it is essential to configure connection pool monitoring for a backend storage like MySQL in a production environment.

How should we improve?

We have configured monitoring for the MySQL backend in production. You can assign this to me, and I will complete it.

[xloya]

It's a useful feature, maybe we can report the connection pool metrics to the prometheus (already used by the API metrics). By the way, from my current feeling, this feature requires multiple PRs to complete, maybe you can list the sub tasks firstly.