Add derivatives available flag to dataset level in search

[nellh]

Is your feature request related to a problem? Please describe. Allow you to search for any datasets that have any snapshots with derivatives recorded.

Describe the solution you'd like The datasets object has a new top level field that indexes all snapshots for any derivatives that are available. Search exposes a boolean field to filter for this field.

Describe alternatives you've considered This is dataset wide instead of per snapshot to ensure newly published snapshots do not prevent you from finding existing derivatives.

Additional context Snapshot object may need to expose the actual derivative dataset linking information to implement this.