Extensible healthcheck

[hmbacher]

Hi @theelims, this PR contains now contains:

Add extensible health check endpoint Introduces a new /rest/health endpoint that enables monitoring of device state, health, and availability from external monitoring systems.

Key features:

• Default response: Returns { "up": true } out of the box
• Extensible design: Supports custom callback functions to add dynamic health information per request
• Lightweight: Minimizes data transfer by allowing customizable content tailored to specific monitoring needs
• Flexible: Can be extended with application-specific health metrics without modifying core functionality