Complete Opportunities Search Backend Implementation.

[JayPalm]

The search_opportunities endpoint is currently unable to search future opportunities in the Umbra constellation.

Remaining work:

• Add method to convert returned feasibilities from Umbra into STAPI Opportunities
• Convert opportunity parameters from cql2 filter format to match Umbra's Feasibility Request format.
• Abstract out logic for the two types of products (umbra_archive_catalog and umbra_spotlight) to simplify search_opportunities