Implement Filter Extension

[philvarner]

Related Issue(s):

• Implement Filter Extension - Basic CQL2 conformance classs #27

Description:

• Implements Filter Extension as GET with CQL2-Text and POST with CQL2-JSON, supporting the Basic CQL2 and Basic Spatial Operators conformance classes.

PR Checklist:

• Code is formatted and linted (run pre-commit run --all-files)
• Tests pass (run make test)
• Documentation has been updated to reflect changes, if applicable, and docs build successfully (run make docs)
• Changes are added to the changelog

[gadomski]

LGTM. Does seem like stac_fastapi/elasticsearch/stac_fastapi/elasticsearch/extensions/filter.py is general enough to (eventually) pull out to its own thing if/when that makes sense?

[philvarner]

I see the long-term plan is to rewrite this simple implementation using the pygeofilter AST. I didn't realize their implementation was that complete and composable until I went to use the text->json conversion methods.