[Feature] Add ability to filter scenes by scene_index

[sleetx]

The scene_index field on a scene is the scene number within a group/movie. There doesn't appear to be a filter for this in the UI or GraphQL. I would like to query a list of scenes with a null scene_index value.

The "sceneUpdate" mutation allows for the scene_index field to be modified, but I don't see a corresponding query.

[ariv-x]

Maybe something to add to the "is missing" filter.