Accommodate for satellite data storing coord transform reference as a coordinate

Satellite data uses geostationary coordinates, which means it needs a reference point (satellite position) to transform to lat lon correctly. We currently store this as an "area" attribute, which leads to some problems (for now only in IODC service, read more in this satip issue).

We will be moving to a more robust way of storing this, as a time-dependent coordinate (see this issue in sat consumer). It will be a bit before this is implemented, but we will need to accommodate for it in code here in ocf_data_sampler/select/geospatial.py. We will keep the attribute method as well for backwards compatibility.

This issue is on hold until the sister issue in sat consumer is completed.

Start by reading ocf_data_sampler/select/geospatial.py around lines 123-133, then review the linked satellite-consumer issue to understand the time-dependent coordinate representation. The work is done when geostationary data can use that coordinate reference while retaining support for the existing area attribute; the issue is currently on hold until the sister issue is completed.