add effect selector in dev tools service on Light

[Mariusthvdb]

please see: home-assistant/core#68607 (comment)

on certain Hue lights, we now have Effect. However, in order to be able to set that via the dev tools Service page, we need to know the exact name of the effect.

It would be very nice if the service page could have a selector with the available options

[Mariusthvdb]

quoting the explanation I got in Discord #beta

That'd be a pretty big architectural change, given that the backend specifies the details of the selector at startup from a static yaml file, and gets no information about what entities are selected as the target.
Same reason select.select can't even offer a dropdown of select options.