[DF] Add Selective Aggregates - Filter

[jdye64]

Is your feature request related to a problem? Please describe.
Apache Datafusion cannot currently parse the Filter syntax of a selective aggregate query. The current implementation with Apache Calcite does support this functionality. We need to add this support to Dask-SQL using Datafusion to ensure that we honor a non-breaking backing SQL implementation.

More information about the Filter clause can be found at Filter Clause Documentation

Describe the solution you'd like
test_groupby.py and aggregate.py currently have commented out code due to this functionality missing in Datafusion. Once Datafusion adds the needed fields and support, Datafusion Issue that code needs to be un-commented and tested for validity. There is likely to be some small refactoring needed in logical.rs and aggregate.rs as well to account for the new Datafusion struct member holding the filtering conditions.

Describe alternatives you've considered
A clear and concise description of any alternative solutions or features you've considered.

Additional context
This feature request depends on this Datafusion issue first being resolved.