Improve JDBC Driver Documentation

**User story**
As a citrus user, I would like to find a step by step guide of how to add the Citrus JDBC driver to my application.

**Additional context**
It's not obvious how to obtain the driver, how it should be added to the application, etc.

The issue does not name a documentation file or test. First locate the existing JDBC driver documentation and the Citrus JDBC driver entry points, then document how to obtain the driver and add it to an application; done means a user can follow a complete step-by-step guide.

Written by the indexing model from the issue text.