Update references of deprecated com.mysql.jdbc.Driver

MySQL Connector/J version 8 deprecates com.mysql.jdbc.Driver in favor of com.mysql.cj.jdbc.Driver, see https://dev.mysql.com/doc/connector-j/8.0/en/connector-j-api-changes.html.

Since the default Dockerfile has
   ENV MYSQL_DB_DRIVER com.mysql.jdbc.Driver 
it produces on startup:

Loading class `com.mysql.jdbc.Driver'. This is deprecated. The new driver class is `com.mysql.cj.jdbc.Driver'. The driver is automatically registered via the SPI and manual loading of the driver class is generally unnecessary.

There's also a reference in https://documentation.bloomreach.com/library/deployment/set-environment-specific-configuration-with-docker.html