[firebase_messaging] set notification channel id (notification in background Not working)

[MahmoodBakhshayesh]

Describe the bug
the function onResume and onLunch not working on android platform, while they work fine on IOS,
i receive the following message on console instead of printed strings in those functions:

"W/FirebaseMessaging(24847): Missing Default Notification Channel metadata in AndroidManifest. Default value will be used."

onMessage function works fine, the problem is when the app is in background

To Reproduce
try to print something in onResume and onLunch functions

Expected behavior
the functions be called on work fine as they do on IOS

Additional context
my guess is that it has something to do with android notification channel id which should be added in android manifest

when i add that to manifest the message change to :
"Notification Channel set in AndroidManifest.xml has not been created by the app. Default value will be used."

[kroikie]

@MahmoodBakhshayesh Thanks for flagging this, looks like we don't currently have support for message channels. We should add this.

Feel free to submit a PR if you have a solution.

[iapicca]

#47
#53
#116
#125