expose spatial_extents in collection properties

[utas-amberbian]

Pass spatial_extents from the STAC document through to the collection response:

"properties": {
  "spatial_extents": [
    { "description": "Pelorus Reef - 5479 Currents / Waves", "bbox": [146.49924, -18.5391, 146.49924, -18.5391] }
  ]
}

The portal will show this in a popup on the details map (aodn/backlog#8805).

Only the single-collection endpoint returns it. Search results don't, so list responses stay small.

Notes

• Merge the es-indexer PR first, then bump stacmodel here to the new release — this PR does not compile against the current 0.0.66.