[DOC] document databricks init script required for UCX

[abellina]

We have a databricks RapidsShuffleManager shim, and we also have been able to run with UCX in databricks, but the documentation hasn't been updated to both expose the 301db and 311db settings, and include the documentation for the init script required to install UCX in that environment.

Note this would be for the user-space parts to get the shuffle manager to work, not necessarily to run with RoCE/Infiniband (I know Azure supports that, but I do not know how common a setup that is).