feat(api): change user appointment stats endpoint to POST method

Changed the user_appointment_stats endpoint from GET to POST method
and added email as a required field. This change allows for more
flexible querying of appointment statistics by requiring user email
in the request body rather than URL parameters.

BREAKING CHANGE: The /api/meetings/user/appointments/stats/ endpoint
now accepts POST requests instead of GET and requires an email field
in the request body.

booking_system/views.py

@@ -297,8 +297,9 @@ def api_root(request, format=None):
         "user_appointment_stats": {
             "description": "Get appointment statistics and analytics for the authenticated user",
             "url": request.build_absolute_uri("/api/meetings/user/appointments/stats/"),
-            "methods": ["GET"],
+            "methods": ["POST"],
             "authentication": "Required",
+            "required_fields": ["email"],
             "response_fields": {
                 "total_requests": "Total number of appointment requests",
                 "pending_review": "Number of pending review requests",