Feature/8432 add search query explain

[shaunahu]

Changes

• Add GET /api/v1/ogc/admin/explain
  • explains normal collection search results
  • returns the Elasticsearch request, total hits, hit IDs, scores, and score explanations

• Add GET /api/v1/ogc/admin/explain/{uuid}
  • explains whether one Elasticsearch document (uuid) matches the query

• Add a config flag:
  • ogcapi.debug.elasticsearch-explain-enabled
  • disabled by default
  • enabled for dev and test

Notes:
This API is for debugging only. So we add a config flag ogcapi.debug.elasticsearch-explain-enabled in application-*.yml. It is enabled for dev and test, and disabled by default. So in edge/staging/production environments, when call these endpoints, it will return 404 error. We will further enable the admin endpoints for these environments after we make firewall changes.

[utas-raymondng]

LGTM