fix(types): add missing map_booking_labels to Settings interface

The booking-labels toggle from the transport-routes-on-map change was
reading and writing settings.map_booking_labels without the key being
declared on the Settings type, so the store typing was inconsistent.
Adds it as an optional boolean to match the other display toggles.

client/src/types.ts

@@ -212,6 +212,7 @@ export interface Settings {
   show_place_description: boolean
   route_calculation?: boolean
   blur_booking_codes?: boolean
+  map_booking_labels?: boolean
 }
 
 export interface AssignmentsMap {