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

### 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.

Start by locating the Java implementation of Gravitino's MySQL backend connection pool and the configuration for maxConnectCount and maxIdleConnect. Review how backend storage is initialized and how production monitoring is configured. Done means the pool parameters are configurable and relevant connection-pool metrics are exposed and verified.

Written by the indexing model from the issue text.