Document process to remove drivers

**Is your feature request related to a problem? Please describe.**
We have some customers who use Metabase and just need 1 driver bundled (along the mariadb/postgres ones) in the Uberjar. Right now our build process includes all of the supported ones, or even if you just add only one, you still get the dependencies bundled.

It would be great if we could document how to remove drivers that are not used by our customers and also its dependencies, so they get the lightest uberjar possible

**Describe the solution you'd like**
Document how to remove drivers and dependencies

**Describe alternatives you've considered**
NA

**How important is this feature to you?**
Important for some of our customers

**Additional context**
NA

No files or tests are named. Start by locating the Uberjar build configuration and the driver and dependency definitions, then document the process for excluding unused drivers and their dependencies. Done means a customer can follow the documentation to produce an Uberjar containing only the drivers they need.

Written by the indexing model from the issue text.