feat: firebase cloud messaging 추가 (#46)

Author: Neibce

frontend/ongi/firebase.json

@@ -0,0 +1 @@
+{"flutter":{"platforms":{"android":{"default":{"projectId":"ongi-3841c","appId":"1:836191706644:android:aee724fe64fc84cbc1d101","fileOutput":"android/app/google-services.json"}},"ios":{"default":{"projectId":"ongi-3841c","appId":"1:836191706644:ios:ea2c1dc070183aa3c1d101","uploadDebugSymbols":false,"fileOutput":"ios/Runner/GoogleService-Info.plist"}},"dart":{"lib/firebase_options.dart":{"projectId":"ongi-3841c","configurations":{"android":"1:836191706644:android:aee724fe64fc84cbc1d101","ios":"1:836191706644:ios:ea2c1dc070183aa3c1d101"}}}}}}