implement error and healthh endpoints

lib/provider_service_web/controllers/health_controller.ex

@@ -0,0 +1,15 @@
+defmodule ProviderServiceWeb.HealthController do
+  use ProviderServiceWeb, :controller
+
+  def health(conn, _params) do
+    conn
+    |> put_status(:ok)
+    |> json(%{status: "ok"})
+  end
+
+  def ready(conn, _params) do
+    conn
+    |> put_status(:ok)
+    |> json(%{status: "ready"})
+  end
+end