Added delay to retry connection

[camcima]

When a consumer connection breaks, aiokafka goes into a loop trying to reconnect every 1ms, generating a mountain of logs. This PR introduces a delay between connection attempts with the configured retry_backoff_ms parameter.

Addresses issues #496 and #830.

[jainal09]

Is it possible to have the functionality at the user level where we can catch these network connection errors. Because even with exponential back off it will keep retrying indefinitely

[mashkovd]

#496
I wrote about this issues.
@ods can you review it? thx

[ods]

#496 I wrote about this issues. @ods can you review it? thx

Sorry, my competence is not enough to propose a correct fix to the problem. The suggested change looks rather like a quick-n-dirty workaround. I hope @tvoinarovskyi finds time to take a look.