rework documentation for pydantic models of sentinel groups

[d-v-b]

#105 removes some useful markdown documentation of the pydantic models for sentinel 1 and 2 groups because the example datasets are offline, and new datasets reveal limitations in the models that need to be addressed. After #105 is merged, we need to revisit this and fix the underlying issues with the pydantic models (or just update the documentation to new structure)