Add test push notification flow

lib/push-store.ts

@@ -31,6 +31,10 @@ export function getPushSubscriptions() {
   return Array.from(getStore().subscriptions.values());
 }
 
+export function getPushSubscription(endpoint: string) {
+  return getStore().subscriptions.get(endpoint) ?? null;
+}
+
 export function hasSentWarning(endpoint: string, warningId: string) {
   return getStore().sentWarningIds.get(endpoint)?.has(warningId) ?? false;
 }