make provider config simpler

lib/policy_service/application.ex

@@ -5,12 +5,10 @@ defmodule PolicyService.Application do
 
   use Application
 
-  defp get_zitadel_config(key) do
-    Application.get_env(:policy_service, :zitadel)[key]
-  end
-
   @impl true
   def start(_type, _args) do
+    zitadel_config = Application.get_env(:policy_service, :zitadel, [])
+
     children = [
       PolicyService.CommandedApp,
       PolicyService.Handlers.QuoteRequestHandler,
@@ -25,7 +23,7 @@ defmodule PolicyService.Application do
       {Phoenix.PubSub, name: PolicyService.PubSub, pool_size: 1},
       {Oidcc.ProviderConfiguration.Worker,
        %{
-         issuer: get_zitadel_config(:issuer),
+         issuer: Keyword.get(zitadel_config, :issuer),
          name: PolicyService.ZitadelProvider
        }},
       PolicyServiceWeb.Endpoint