re-subscribe logic

1. Re-subscribe logic in registry handler that loops subscription logic for 3 times
2. Addresses gson serialization issue by providing a simple typeadapter for handling fields of type 'class' as seen in 'Modify' -type change notification.
This means on reconnect you will write the same messages again on the same websocket connection.
You must send a reset message to the client if you want transparent retries. OTOH, you can propogate the error to the dashboard which then can retry. In this setup, it will be very convoluted for you to manage state on the connection once there is an error in the stream from eureka client.