[Feature Request] Add appAccountToken parameter to identify() method in Flutter SDK

[alexkorolchuk]

The iOS native SDK supports appAccountToken since v3.10.2:
Adapty.identify(customerUserId, withAppAccountToken: uuid)

But Flutter SDK doesn't have this parameter:
await Adapty().identify(customerUserId); // ❌ no appAccountToken

Please add:
await Adapty().identify(customerUserId, appAccountToken: uuid); // ✅

This is critical for:

1. Proper webhook handling from Apple (appAccountToken in transactions)
2. Matching purchases to correct user accounts
3. Preventing subscription sharing abuse

[x401om]

Hi @alexkorolchuk! We're going to introduce this parameter in the upcoming release.