Update saved_queries and group_by (#4473)

## What are you changing in this pull request and why?
Update the saved query spec to conform with the user input core expects.

website/docs/docs/build/saved-queries.md

@@ -19,14 +19,14 @@ To define a saved query, refer to the following specification:
 The following is an example of a saved query:
 
 ```yaml
-saved_query:
+saved_queries:
   name: p0_booking
   description: Booking-related metrics that are of the highest priority.
   query_params:
     metrics:
       - bookings
       - instant_bookings
-    group_bys:
+    group_by:
       - TimeDimension('metric_time', 'day')
       - Dimension('listing__capacity_latest')
     where: