We need our own anonymous ID for Flutter App

[SeanYHwang]

We are using this for Flutter App.

I am looking for like setAnonymousId() method. But, I notice there is no support for this function in the current version of analytics_flutter. In our app, we are generating the anonymousId, so we want to reuse this for the identify() call.

It would be good to extend the identify() or another setAnonymousId() method for the analytics.