use actioncable to track indexing progress
closes #3049
Does this impose a new Redis dependency on everyone who wants to run Spotlight?
@jcoyne Yeah but the way I understood it, it was already a dependency of spotlight?
@dnoneill redis is not a dependency of spotlight as far as I know.
@dnoneill could this please link to an issue that says what / why
moving into draft. Got 90% of the way to moving all the actioncable stuff into the engine. Unfortunately we couldn't figure out how to import channels/consumer into sprockets without it erroring.
It also checks for actioncable, if not falls back to previous behavior.