Do not save read-only attributes, unknown/unavailable states, ... in scenes

When creating scenes from the UI, every single attributes of entities and every entities linked to a device a saved in the scene, even when it doesn’t make sense.

Examples:

  • Read-only attributes (e.g. light effect list): Not relevant when restoring a scene, obviously
  • Entities with unknown/unavailable states
  • Button entities (“Warning: Integration button does not support reproduce state”)

Besides giving errors when trying to restore those states, it makes them difficult to edit in YAML.

Basically, this FR for making the “create scene” in UI smarter :wink: