Consider adding isServiceAvailable to PushService

[jonalmeida]

Adding this method to the PushService will make the implementation across various applications easier to follow.

API:

interface PushService {
  fun isServiceAvailable(context: Context): Boolean
}

┆Issue is synchronized with this Jira Task

[jonalmeida]

This has come up again during ADM integration with Fire TV. Since we own the ADM instance, it makes sense for us to provide this functionality and checks for the app.

Implementing the same for the Firebase should be straight-forward from the old patch.