Automatic failover for Devices

## High Availability & Scaling Epic
https://github.com/flowforge/flowforge/issues/1678

### Related Issue for Instances
https://github.com/flowforge/flowforge/issues/1920

## Description
Implement a robust automatic failover mechanism for Devices

### Draft
- Implement a feature within the device agent that allows configuration to indicate that two devices are meant to work in a pair - a primary device and a backup (or 'spare') device. This 'hot spare' approach allows for an immediate switch to the backup device if the primary device fails.
- Develop a procedure to keep these paired devices synchronized. This procedure should ensure that all relevant device data, configurations, and operational parameters are kept updated between the primary and backup device.
- Incorporate a health monitoring system to continually assess the operational status of the devices. This information should be made accessible via an API or Broker to facilitate integration with other systems.
- Provide a guide on how to set up a Nginx configuration that can distribute network traffic between the primary and backup devices.