OpenAPI: make it possible to generate a spec without starting the app

Needed for api docs generation on pleroma.social that will come later

lib/pleroma/web/api_spec.ex

@@ -13,10 +13,15 @@ defmodule Pleroma.Web.ApiSpec do
   @impl OpenApi
   def spec do
     %OpenApi{
-      servers: [
+      servers:
+        if Phoenix.Endpoint.server?(:pleroma, Endpoint) do
+          [
             # Populate the Server info from a phoenix endpoint
             OpenApiSpex.Server.from_endpoint(Endpoint)
-      ],
+          ]
+        else
+          []
+        end,
       info: %OpenApiSpex.Info{
         title: "Pleroma",
         description: Application.spec(:pleroma, :description) |> to_string(),