Add custom state as an additional parameter in iOS

[nsaechao]

For android, there is a way to override the state parameter #587 which can be overridden by specifying a state field in additionalParameters.

[Jay-A-McBee]

👋 hey @nsaechao

This sounds like a good idea!

Would you be willing to get a PR together that implements this? The main thing to consider is the immutability of NSDictionary. We'd need to copy additionalParameters to a NSMutableDictionary in order to remove the "state" object. This would be in line with the Android implementation. Thoughts?

Look forward to hearing from you 🚀

[kadikraman]

Should be resolved in #735