Short-circuit API rate limiter for unauthenticated users (#607)

### Major
- Short-circuit API rate limiter for unauthenticated user
  Calls by unauthenticated users were failing at API rate limiter as it
  failed to access user info object. This is a bug.
  
  API rate limiter should short-circuit for unauthenicated users so a
  proper Forbidden response can be returned by API
  
  Add regression test to verify that unauthenticated users get 403
  response when calling the /chat API endpoint
  
### Minor
- Remove trailing slash to normalize khoj url in obsidian plugin settings
- Move used /api/config API controllers into separate module
- Delete unused /api/beta API endpoint
- Fix error message rendering in khoj.el, khoj obsidian chat
- Handle deprecation warnings for subscribe renew date, langchain, pydantic & logger.warn

pyproject.toml

@@ -55,7 +55,7 @@ dependencies = [
     "torch == 2.0.1",
     "uvicorn == 0.17.6",
     "aiohttp ~= 3.9.0",
-    "langchain >= 0.0.331",
+    "langchain <= 0.2.0",
     "requests >= 2.26.0",
     "bs4 >= 0.0.1",
     "anyio == 3.7.1",