[event-hubs] add downtime recovery sample

[chradek]

/cc @ramya-rao-a

This is a rough sample of how a user could keep track of MessagingErrors and decide to recreate their EventHubConsumerClient.

The DowntimeTracker is super simple. It just keeps track of the timestamps when isDown() is called. It also accepts a "maximumAllowedDowntimeInSeconds" parameter in the constructor that basically sets the threshold where if we see errors for longer than this period, we consider the client 'down'.

For this to work properly, the user also needs to call downtimeTracker.clear() when they do receive an event to indicate that the downtime ended.

It needs some disclaimers and I wasn't sure where exactly is the best place to put it but for now added it as a sample.

[ghost]

Hi @chradek. Thank you for your interest in helping to improve the Azure SDK experience and for your contribution. We've noticed that there hasn't been recent engagement on this pull request. If this is still an active work stream, please let us know by pushing some changes or leaving a comment. Otherwise, we'll close this out in 7 days.

[ghost]

Hi @chradek. Thank you for your contribution. Since there hasn't been recent engagement, we're going to close this out. Feel free to respond with a comment containing "/reopen" if you'd like to continue working on these changes. Please be sure to use the command to reopen or remove the "no-recent-activity" label; otherwise, this is likely to be closed again with the next cleanup pass.