Phoenix.PubSub-backed adapter. Delegates to a user-supplied Phoenix.PubSub
server name configured via:
config :council_ex, pubsub: {CouncilEx.PubSub.Phoenix, name: MyApp.PubSub}CouncilEx does not start the Phoenix.PubSub server; the host application is
responsible for placing {Phoenix.PubSub, name: MyApp.PubSub} in its own
supervision tree.