Event Handling Support on the Application Layer

[suggestedfixes]

Currently, there isn't a way to send events to the application layer. One possible approach is to support GStreamer events so that the application layer can handle events. But any other mechanism that allows for easy event handling would be helpful.

[MushMal]

I agree that this is super important for any involved application using KVS GStreamer plugin.

To add a few notes on the events.

• Report any errors during streaming
• Report any error ACKs coming back
• Report any API call failures like putFrame/putMetadata, etc..
• Report most of the callbacks (informative or pressures) so the applications can react.