allow selecting queryables per collection

[mhogeweg]

Queryables may be defined at the root of the STAC and per collection. Currently, all collections have the same set of queryables. With this enhancement, users may select queryables from the root set of queryables (stac/queryables). The selected queryables become the queryables for the collection accessible via stac/collections/{collectionId}/queryables.

This selection may be implemented in the Collections panel. The keys of selected queryables are stored in a list in the collection's JSON. for example:

{
  "extent": {
    "spatial": { ... },
    "temporal": { ... }
  },
  "stac_version": "1.0.0",
  "keywords": [],
  "type": "Collection",
  "title": "The Collection",
  "properties": {
    "queryables": [ "queryableKey1", "queryableKey2", ...]
  }
  ...

If no collection-specific queryables property is defined or it is an empty list, all querables from the root are included.