[PBE 6041] Fix incoming call PN issue

[liviu-timar]

🎯 Goal

Fix issue that makes incoming call PN to not be delivered after user logs-out and a new user logs-in.

🛠 Implementation details

• Always re-assign the Retrofit API instance when installing StreamNotificationManager so that the correct user token is used in the AuthInterceptor for CreateDevice and DeleteDevice requests.
• Register the push device only after getting connection.ok event to avoid race-condition between VideoConnect and CreateDevice.
• Fix the Demo App by calling deleteDevice at log-out.

🧪 Testing

• Sign in with a user and see if it receives incoming call PN.
• Sign out then sign in again with another user. The new user should also get the PN and be able to accept the call.
• Can be done in the Demo App or in the Audio Call Sample.