MySqlFirehoseDatabaseConnector uses configured driver class name

[suneet-s]

Description

If a user configures Druid to use the mariadb driver instead of mysql, they would also need to update the mysql input source to tell it to use the mariadb driver to get ingestion to succeed.
Since we're already asking users to choose their driver in the mySQLConnectorDriverConfig, we use this driver instead of trying to guess the driver based on the connectURI.

This was found by the ITSqlInputSourceTest yay integration tests! :)
This PR has:

• been self-reviewed.
• added documentation for new or modified features or behaviors.
• added comments explaining the "why" and the intent of the code wherever would not be obvious for an unfamiliar reader.
• added unit tests or modified existing tests to cover new code paths, ensuring the threshold for code coverage is met.
• added integration tests.
• been tested in a test Druid cluster.