Bugfix/disconnect due to slow consumer event drop

[kashyap-splunk]

Adding mechanism to drop events if the events queue is full to avoid the blocking of the main nozzle goroutine and hence avoid passing the back pressure back to Doppler when the downstream is slow.

There is still room to further improve it by moving the event parsing from main thread to writer threads. This will be addressed in later pull-requests targeted in subsequent releases.

[luckyj5]

How far did we test it? Did we test it with reproducible scenario with slow-consumers errors on tc?

[kashyap-splunk]

How far did we test it? Did we test it with reproducible scenario with slow-consumers errors on tc?

Yes, tested with a low values of the queue size and HEC workers to reproduce the errors while reading and verified that the new build drops events in the same scenario instead of any errors from web-socket.