Multiple SenderIDs/FCM projects?

**Is your feature request related to a problem? Please describe.**
Maybe? I have an app that I don't want to ship credentials with. Instead, I want the app to contact a server to discover the FCM details for SenderID etc. My app can connect to a self hosted server setup, so I want to support self hosted users using FCM. I think this is possible today using native FCM and calling getToken after GETing a senderID.

**Describe the solution you'd like**
I'd like to have my app be able to initialize FCM's config (senderID specifically) in JS on iOS and Android. I currently do this today for the PWA. Ideally I wouldn't have to provide the FCM credentials as a plist or JSON file, but I'm fine doing that if I can overwrite those values in JS.

**Describe alternatives you've considered**
I think it's fine if I can't do this, but it would be really cool if it works!!

**Additional context**

Start by inspecting the plugin's existing iOS and Android FCM configuration and token initialization entry points. Determine whether a sender ID can be supplied from JavaScript after startup, and define done as supporting the requested runtime configuration on both platforms without requiring fixed platform credentials.

Written by the indexing model from the issue text.