Move api_key resolution to OpenAI module

lib/open_ai.ex

@@ -4,7 +4,7 @@ defmodule OpenAI do
   def gpt(completion) do
     {:ok, collector} = Agent.start_link(fn -> "" end)
 
-    API.gpt_stream(completion, fn data ->
+    API.gpt_stream(completion, api_key(), fn data ->
       case get_in(data, ["choices", Access.at(0), "delta", "content"]) do
         nil -> :ok
         data -> Agent.update(collector, fn current -> current <> data end)
@@ -15,4 +15,9 @@ defmodule OpenAI do
     Agent.stop(collector)
     {:ok, result}
   end
+
+  defp api_key do
+    Application.get_env(:music_library, __MODULE__)
+    |> Keyword.fetch!(:api_key)
+  end
 end