AD-627 - Error handling and auto recovery of connection failures on producer side

Fixes first phase of https://aclgrc.atlassian.net/browse/AD-627 - log and recover from message queue server downtime on producer side.

Didn't make change for consumers yet as there is less urgent need and we should test one thing at a time.
This handler is actually used both in cases where connection to mq server can't be established on startup, and when it can't be established during a request. So using the word 'connection' is IMO appropriate here.