Add Google Chat

[jpbalda]

This PR adds support for Google Chat notifications.

Currently major platforms are supported, however, I think Google Chat is missing and could be very beneficial for many users. The implementation is similar to the existing ones.

Here is an example:

@success
    @googleChat($webhookUrl, 'hola')
@endsuccess

And this is the result in Google Chat

[taylorotwell]

Thanks for your pull request to Laravel!

Unfortunately, I'm going to delay merging this code for now. To preserve our ability to adequately maintain the framework, we need to be very careful regarding the amount of code we include.

If applicable, please consider releasing your code as a package so that the community can still take advantage of your contributions!