use external secrets for password generation

config/runtime.exs

@@ -20,6 +20,10 @@ if System.get_env("PHX_SERVER") do
   config :policy_service, PolicyServiceWeb.Endpoint, server: true
 end
 
+if cookie = System.get_env("RELEASE_COOKIE") do
+  config :elixir, :cookie, cookie
+end
+
 config :policy_service, PolicyServiceWeb.Endpoint,
   http: [port: String.to_integer(System.get_env("PORT", "4000"))]