Added feature in weather-mv to extract specific date's data from zarr files.

[dabhicusp]

I have added a feature in weather-mv which can allows users to access data for a specific date from Zarr files. In the existing codebase user have no choice for working with some chunks of the zarr file so user have to work with whole zarr file every time.
One use-case: If user want to ingest specific date's data from the zarr file to BQ then he/she can do this using of this code.

[alxmrs]

Suggested change

	start_date = open_dataset_kwargs['start_date']
	if open_dataset_kwargs is not None:
	open_dataset_kwargs.pop('start_date', None)
	start_date = open_dataset_kwargs.pop('start_date', None)

[dabhicusp]

Hi @alxmrs, it's important to ensure that a open_dataset_kwargs is dictionary or not before using the pop operation directly on it. As in the code on this line mentioned that it is a optional value & default value of it is None.

[mahrsee1997]

LGTM.

[alxmrs]

Perfect, change looks great!