fix(core/pygeoapi): add feature provider to Water Chemistry & Water Levels (BDMS-1536) - #1046

Why

This PR addresses the following problem / context:

• CSV exports for Water Chemistry fail with HTTP 400: Invalid provider type.
• The /ogcapi-internal/collections/{collection}/items endpoint requires a feature provider, but Water Chemistry and Water Levels previously registered only EDR providers.
• The frontend relies on the GeoJSON /items response to generate CSV downloads.

How

Implementation summary: the following was changed / added / removed:

• Added feature providers alongside existing EDR providers for Water Chemistry and Water Levels.
• Extended DescribedPostgreSQLProvider to construct GeoJSON point geometries from longitude and latitude fields when no geometry column exists.

Author Checklist

• Changes are limited to the intended scope.
• Tests were added or updated where appropriate.
• Relevant tests and lint checks pass.
• No secrets, credentials, or sensitive data were publicly exposed.
• Documentation was updated where necessary.

Reviewer Checklist

• Verify CSV exports for Water Chemistry and Water Levels.
• Confirm /items returns valid GeoJSON with point geometry and expected properties.
• Verify limit/offset pagination and bounding-box filtering.
• Confirm internal authentication and public publication filtering remain enforced.
• Confirm existing EDR endpoints continue functioning.

Notes

Any special considerations, known limitations, risks, workarounds, or follow-up work to note?

• The fix is implemented but has not been verified end-to-end.
• Preview CSV downloads remain untested.
• Feature providers reuse existing database views; no frontend changes are needed.