[CM-2026] Added Support for EU Servers

[AbhijeetRanjan308]

Summary

• Added Support of changing server config.

  KommunicateFlutterPlugin.setServerConfiguration("euConfiguration");

• To use this need to add this before using any "Login as Visitor, Login User or Build conversation" in Android.
• To use this iOS side need to add the configuration at didFinishLaunchingWithOptions and before any of these "Login as Visitor, Login User or Build conversation". (Reason: when the app is Closed and reopened at that time the server got reset to default. To overcome the issue we can add the config in AppDelegate didFinishLaunchingWithOptions.)
• After Logout it's necessary to set server again before performing "Login as Visitor, Login User or Build conversation"
• Updated the deprecated function in iOS.