Better control over security features

[TimoGlastra]

Currently this library just exposes an option whether keys should be biometry backed.

I think it would be great if we can expose a better API for creating keys that allows to set the security configuration of a key.

It would be great if this library can be used for a range of different usages, where you just want to leverage the crypto from the native platform.

I think platform specific options is also fine here. Or as Expo often does, try to have cross-platform options, and then add platform specific options where it makes sense.