Add editor support for always_error_if_entity_unavailable

[dermotduffy]

          @dermotduffy, the feature works amazing! The card goes into unavailable if the camera entity is unavailable, and even recovers itself gracefully once the entity is back. Also, the card goes to unavailable even if during operation the entity goes unavailable.

Setting it in cameras_global makes it very easy to configure for me.

Something I did not understand why is: I could not find it anywhere in the UI configuration. But adding to YAML worked. I'm not sure if that's intended. Maybe I just didn't find it.

Originally posted by @felipecrs in #1770 (comment)