When a websocket PUSH connection is closed and re-established because
of a network failure, the RequestResponseTracker.hasActiveRequest is
not reset, prenvint the Flow client to send additional messages to
the server.
This change will reset the flag on reconnection. It also will track
unsent PUSH message over websocket, to retry the delivery once the
connection is re-established, preventing client resynchronization.
In addition, it sets a default value of 12 for the Atmospehere
maxWebsocketErrorRetries setting, to ensure that the Flow client will
attempt to reconnect with web socket transport several times, instead
of immediately downgrade to long-polling after first failed connection.

Fixes #20213