Standardize construction of websocket URL

This follows up on the change made in d747bd98

lib/pleroma/plugs/http_security_plug.ex

@@ -35,7 +35,7 @@ defp headers do
   defp csp_string do
     scheme = Config.get([Pleroma.Web.Endpoint, :url])[:scheme]
     static_url = Pleroma.Web.Endpoint.static_url()
-    websocket_url = String.replace(static_url, "http", "ws")
+    websocket_url = Pleroma.Web.Endpoint.websocket_url()
 
     connect_src = "connect-src 'self' #{static_url} #{websocket_url}"
 

lib/pleroma/web/mastodon_api/mastodon_api_controller.ex

@@ -1295,8 +1295,7 @@ def index(%{assigns: %{user: user}} = conn, _params) do
       initial_state =
         %{
           meta: %{
-            streaming_api_base_url:
-              String.replace(Pleroma.Web.Endpoint.static_url(), "http", "ws"),
+            streaming_api_base_url: Pleroma.Web.Endpoint.websocket_url(),
             access_token: token,
             locale: "en",
             domain: Pleroma.Web.Endpoint.host(),