feat: support created_at filter for the GET /users endpoint (#15633)

Closes https://github.com/coder/coder/issues/12747

We support these filters currently:
https://coder.com/docs/v2/latest/admin/users#user-filtering, adding
`created_at` filter as well.

coderd/database/modelqueries.go

@@ -391,6 +391,8 @@ func (q *sqlQuerier) GetAuthorizedUsers(ctx context.Context, arg GetUsersParams,
 		pq.Array(arg.RbacRole),
 		arg.LastSeenBefore,
 		arg.LastSeenAfter,
+		arg.CreatedBefore,
+		arg.CreatedAfter,
 		arg.OffsetOpt,
 		arg.LimitOpt,
 	)