Feat/dhis2 query pushdown

[abyot]

Summary

This PR strengthens the DHIS2 org-unit collection integration by pushing query work down to DHIS2 while keeping an OGC-facing API shape. It also hardens field projection behavior, adds mapping docs/examples, and reduces local dev noise from Prefect during reload.

What changed

• Centralized DHIS2 org-unit querying through the adapter:
  • Added pass-through query support (query_organisation_units) with configurable params.
• Improved dhis2-org-units provider behavior:
  • OGC CQL filter subset translation to DHIS2 filters (eq, in, like/ilike, and).
  • Pushdown of paging (page, pageSize) when possible.
  • all=true extension mapped to paging=false.
  • Local fallback filtering when CQL cannot be translated.
• Field projection cleanup:
  • OGC properties drives standard projection.
  • dhis2_fields enables dynamic DHIS2-native projection.
  • Enforced required id in projected fields to keep valid GeoJSON features.
  • Added robust parsing for nested DHIS2 fields (e.g. parent[id,name]).
• Enabled forwarding extra query params from pygeoapi to providers:
  • include_extra_query_parameters: true for DHIS2 providers.
• Prefect/dev ergonomics:
  • Added EO_API_ENABLE_PREFECT toggle to disable Prefect app/lifespan in local reload workflows.
  • Improved shutdown handling to reduce cancellation noise.
• Added docs and utilities:
  • docs/dhis2-ogc-mapping-spec.md
  • sample_data/ADM1.geojson
  • scripts/run_chirps3_pipeline_with_geojson.py
• Tests:
  • Expanded tests/test_dhis2_common.py for query options, all=true, ID enforcement, nested field parsing, projection behavior, and CQL translation.

Why

• Avoid fetching everything and filtering locally where DHIS2 can do it server-side.
• Keep the external API OGC-friendly while retaining DHIS2-native power where needed.
• Support richer DHIS2 field use cases (hierarchy fields like path, nested parent[...]).
• Improve local developer experience by avoiding noisy Prefect shutdown traces during --reload.

Example requests

• OGC-style filtering + standard projection:
  • /ogcapi/collections/dhis2-org-units/items?filter=level=2&properties=name,code,level
• OGC filtering + DHIS2-native projection:
  • /ogcapi/collections/dhis2-org-units/items?filter=level=2&dhis2_fields=name,code,level,path,parent[id,name]
• Fetch all matches:
  • /ogcapi/collections/dhis2-org-units/items?filter=level=2&all=true&dhis2_fields=id,name,path,geometry

Notes

• properties remains validated by pygeoapi (strict/OGC-safe).
• dhis2_fields is the intended dynamic projection path for DHIS2-specific fields.