chore: add totalEdges for Postgres snippet

Author: ddebrunner

dbquery/pagination/api.graphql

@@ -26,6 +26,11 @@ the starting point).
 type CustomerConnection {
   edges: [CustomerEdge]
   pageInfo: PageInfo!
+
+  """
+  Total number of edges, may be `null` if the value cannot be determined.
+  """
+  totalEdges: Int
 }
 
 """

dbquery/pagination/operations.graphql

@@ -11,5 +11,6 @@ query Customers($first: Int!, $after: String = "") {
       endCursor
       hasNextPage
     }
+    totalEdges
   }
 }