Ring Camera On/Offline Sensor for HomeBridge
<!--
Please DO NOT DELETE THIS TEMPLATE or your issue may be closed immediately.
Before opening an issue, search for open and closed GitHub issues that match your request.
-->

# Feature Request

### Description
I would like to see a contact sensor surfaced in HomeBridge that shows the online status of Ring cameras. Currently there is no way to be notified that a device is offline using the Ring App.

### Describe the solution you'd like
Create a contact sensor device for each camera/chime in the plugin. When a device is offline for n consecutive polls, mark the contact as open. When the device is online again, mark it as closed.

### Describe alternatives you've considered
I have looked to ring for direct support of this capability, which it does not have. I have also considered using a simple ping tool, however ring devices behind chime pros are essentially NATted devices and are not available to poll this way.

### Device data

