Make ibis backend visible and useful

hvplot has an ibis backend since `0.8.1`. This can be pretty powerful. For example it is potentially a way to connect hvplot and the very popular duckdb.

BUT :-)

There is no

- documentation
- examples
- tests


I.e. users would not know about this killer feature and how to use it.

I've spent the last hour trying to collect the pieces needed. Other users might just leave.

In the end it also seems to me it is not working. See https://github.com/holoviz/hvplot/issues/988

Please add documentation, examples and tests to help me and others get started. Thanks.