FR: Add support for "webpush.fcm_options" (WebpushFcmOptions)

As FCM HTTP API v1  and Firebase JS SDK already supports "[WebpushFcmOptions](https://firebase.google.com/docs/reference/fcm/rest/v1/projects.messages#WebpushFcmOptions)" and [click action handling](https://github.com/firebase/firebase-js-sdk/blob/master/packages/messaging/src/controllers/sw-controller.ts#L189) on Web , I forked this repo and will create a PR for this issue.

