Support subscribing to all channels

[nicholasjhenry]

Registry

Registry.start_link(keys: :unique, name: Registry.SelectAllTest)
iex> {:ok, _} = Registry.register(Registry.SelectAllTest, "hello", :value)
iex> {:ok, _} = Registry.register(Registry.SelectAllTest, "world", :value)
iex> Registry.select(Registry.SelectAllTest, [{{:"$1", :_, :_}, [], [:"$1"]}])
["world", "hello"]

Event Store

https://github.com/commanded/eventstore/blob/master/guides/Subscriptions.md#subscribe-to-all-events

alias MyApp.EventStore

{:ok, subscription} = EventStore.subscribe_to_all_streams("example_all_subscription", self())

# Wait for the subscription confirmation
receive do
  {:subscribed, ^subscription} ->
    IO.puts("Successfully subscribed to all streams")
end

receive do
  {:events, events} ->
    IO.puts "Received events: #{inspect events}"

    # Acknowledge receipt
    :ok = EventStore.ack(subscription, events)
end