Added Topic Creation and Subscription Functionality

[asachanfbd]

FCM topic helps in sending 1 notification(same title and same desc) to large number of users.
Below features are added -

1. Creating a topic
2. Subscribe devices to topic
3. unsubscribe devices to topic.

[Abhi0725]

@brozot Can you please merge this?

[atlkuk]

@brozot I quote the request. Can you merge this? :)

[shiloanton]

why you don’t want to add this functionality, I think it will be very useful

[williamdes]

Hi !
Feel free to re-open this pull-request to code-lts/Laravel-FCM

This is a fork that will be maintained as long as possible by @code-lts members 💪

🚀 1.4.0 was released See how to install it (composer require code-lts/laravel-fcm)

[williamdes]

I would welcome this enhancement on my fork ;)

[Stevemoretz]

I would welcome this enhancement on my fork ;)

I did it for you check your pull request section in your repo.

[williamdes]

Merged as code-lts#5
This one can be closed.