Rework stac api extension logic

[Ariana-B]

Add parameters to SummaryStore.search_items to enable factoring the filter and sortby extensions into the database query, thus moving the logic out of _handle_search_request and search_stac_items in _stac.py, where it was previously causing issues when results were paginated, as highlighted in #579.

Also took the opportunity to fix logic that was missing or out of line with the STAC API spec, such as reported in #536 and initially attempted in #570.

The STAC API extension specs are sometimes unclear or ambiguous around expected behaviour, so I have chosen to interpret them in the ways that seem the most reasonable and consistent. Most notably,

• sortby will ignore any undefined properties,
• both sortby and filter will recognise any potential variant of a property name (stac name (ex: created), eo3 name (ex: odc:processing_datetime), and metadata type search field name (ex: creation_time)) as syntactically valid for that property.

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📚 Documentation preview 📚: https://datacube-explorer--591.org.readthedocs.build/en/591/

[omad]

I think this looks okay, lets just release it and try it...