Extend connect API to handle Viewer's later start or reconnect

[rgolovanov]

Currently, the workflow of the logger-viewer implies that the viewer is running before logging starts, otherwise, it will lead to data accumulation (see #6933 ) and never connect. In practice, it is important to have the ability to know whether connect to the viewer was successful or not and monitor connectivity status somehow.

Describe the solution you'd like

• Extend C++ API to indicate whether connect is successful or not - this would allow users to implement logic which attempts to connect.
• Extend C++ API to indicate that the Viewer has been disconnected - this would allow users to handle such cases and initiate reconnect.

New API interfaces would allow users to handle these cases:

1. Viewer starts after logger: Logger could make periodical checks/attempts to connect and once it is connected, it will start logging.
2. Connected Viewer is closed or restarted: Logger should somehow monitor connection status and switch to periodical checks if the Viewer was disconnected.

[Wumpf]

I don't think this applies to the C++ sdk in particular and is rather an issue in all APIs