datetime in unity-sds-client to_stac should not be forced to equal start_time

[mcduffie]

According to STAC documentation the datetime metadata:

This is likely the acquisition (in the case of single camera type captures) or the 'nominal' or representative time in the case of assets that are combined together. Though time can be a complex thing to capture, for this purpose keep in mind the STAC spec is primarily searching for data, so use whatever single date and time is most useful for a user to search for.

The current code for Collection::to_stac forces datetime to equal start_time. This needs to be changed to respect a user set value.

[mcduffie]

Specifically this line of code: https://github.com/unity-sds/unity-monorepo/blob/main/libs/unity-py/unity_sds_client/resources/collection.py#L113

[rtapella]

@ngachung Mike originally added some of the helper functions for unity-sds-client and STAC. Is this something your team is able to take over?

[ngachung]

Yes, DS will take ownership of this.