subscribeToTopics register to more topics in one call and subscribedTopics to get list of topics already subscribed to

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Hi! My current project has alot of "topics" that users can subscribe to.
One issue that I have seen is that when there are eg 30 topics it would take quite a while to get client registered to all of them.

A subscribeToTopics() would be nice, to get registration time down on the client side.
Similar function exists on serverside; SubscribeToTopicAsync(), it mass register up to 1000 keys to a topic.
Ref: https://firebase.google.com/docs/cloud-messaging/manage-topics

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A subscribedTopics() should return a list of topics this client already registered to.
That would minimize calls to subscribeToTopic