Deprecate notifications threshold

Context

The registry notification system allows a registry to be configured to send events to a given endpoint. The configuration uses the threshold and backoff parameters to specify how many failures are allowed (threshold) before backing off for a given period of time before retrying.

Problem

As seen in fix(notifications): retrying sink does not stop... (#1210 - closed), the event will be held in memory forever until it is successful or the application is shutdown. This is not ideal as it can cause a high memory and CPU usage on the registry side if the events are not sent properly. It will also hold back any new events that are added to the queue of events.

Solution

A new maxretries configuration parameter has been added that can control how many times an event will be retried before dropping the event. As such, we have deprecated the threshold parameter in favor of maxretries so that events are not held in memory forever.