Add Python implementation to support BAGv2 Extract and Mutations

[petersaalbrink]

Is your feature request related to a problem? Please describe.
I use NLExtract for processing the BAGv2 Extract. I'd like to use NLExtract to process BAG Mutations as well. But NLExtract has a dependency on Stetl, and the GDAL BAG-LV driver (which is included with Stetl) does not support processing BAG Mutations.

Describe the solution you'd like
A Python implementation as alternative to the GDAL BAG-LV driver, and an extension of it that supports BAG Mutations.

Describe alternatives you've considered
Alternatives include extending the GDAL BAG-LV driver, or processing BAG Mutations without Stetl.

Additional context
See nlextract/NLExtract#349

[justb4]

This can be useful feature, but belongs to the NLExtract project: nlextract/NLExtract#349. Stetl is a generic ETL library. BAG ETL is domain specific. We can discuss within the NLExtract project.