Add support for a first-party client app to call into Khoj (Part 1) (#601)

* Add support for a first party client app
- Based on a client id and client secret, allow a first party app to call into the Khoj backend with a phone number identifier
- Add migration to add phone numbers to the KhojUser object
* Add plus in front of country code when registering a phone number.
- Decrease free tier limit to 5 (from 10)
- Return a response object when handling stripe webhooks
* Fix telemetry method which references authenticated user's client app
* Add better error handling for null phone numbers, simplify logic of authenticating user
* Pull the client_secret in the API call from the authorization header
* Add a migration merge to resolve phone number and other changes

pyproject.toml

@@ -76,6 +76,8 @@ dependencies = [
     "rapidocr-onnxruntime == 1.3.8",
     "stripe == 7.3.0",
     "openai-whisper >= 20231117",
+    "django-phonenumber-field == 7.3.0",
+    "phonenumbers == 8.13.27",
 ]
 dynamic = ["version"]