Update GeoJSON endpoint to filter by instances with geoms

[KipSigei]

Changes / Features implemented

• Update geojson enpoint to return 404 if all instances/submissions have empty geoms e.g

before

{
  "type": "FeatureCollection",
  "features": [
    {
      "type": "Feature",
      "geometry": {
        "type": "GeometryCollection",
        "geometries": []
      },
      "properties": {
        "id": 111,
        "xform": 20
      }
    }
  ]
}

now

{
  "detail": "Not found."
}

Steps taken to verify this change does what is intended

• Tests

Side effects of implementing this change

Before submitting this PR for review, please make sure you have:

• Included tests
• Updated documentation

Closes #

[DavisRayM]

Can we have this implemented on the model level instead of the viewset ? Guessing this field is updated/set on the model level ?

[KipSigei]

@DavisRayM Moved the logic to the instance model post save signal instead to handle the update after a submission is soft deleted. Note that with soft deletion the post_save signal is triggered instead of post_delete

[DavisRayM]

Let's have this happen in update_xform_submission_count and let's try to avoid a count on the XForm. If possible let's use the Forms submission_count property

[KipSigei]

addressed via 4008f69

[DavisRayM]

This query won't do what is expected; It's counts instances that are not deleted with no geoms... Let's use a query like xform.instances.filter(deleted_at__isnull=True).exclude(geom=None).count() < 1

[DavisRayM]

xform.instances.filter(~Q(geom=None), deleted_at__isnull=True).count() < 1