Implement country filtering for 4D colocated data sets

[lewisblake]

Is your feature request related to a problem? Please describe.
Country filtering is not implemented for 4D colocated data sets.

pyaerocom/pyaerocom/aeroval/coldatatojson_engine.py

Lines 130 to 132 in 1a3c12e

	elif coldata.has_latlon_dims and regions_how == "country":
	raise NotImplementedError(
	"Cannot yet apply country filtering for 4D colocated data instances"

4D colocated data sets are defined as

pyaerocom/pyaerocom/colocation/colocated_data.py

Lines 85 to 88 in 1a3c12e

	cf :func:`pyaerocom.colocation.colocate_gridded_ungridded`) while 4D
	colocated data is created when a model is colocated with another model or
	satellite observations, that cover large parts of Earth's surface (other
	than discrete lat/lon pairs in the case of ground based station locations).

Describe the solution you would like to see
I would like this implemented. Needed for satellite data comparisions, e.g., in SESAM.

• Would you be able to work on this solution yourself? kanskje
• How can the Pyaerocom development team assist you? hjelp

Additional context
Regions in general need an overhaul, but this is a smaller feature which would be very helpful for satellite data comparisons. It isn't obvious to me why this is an issue, but the devil is in the details. This is what such a ColocatedData instance looks like: