Implementing Custom Service Discovery

Prometheus now offers a way to implement custom service discovery integrations without modifying the core Prometheus code. This is achieved through a new adapter pattern, leveraging the internal Discovery Manager and outputting a file format compatible with Prometheus’ `file_sd`. This approach allows users to integrate with service discovery systems not natively supported by Prometheus, while keeping the main Prometheus binary lean and maintainable, and paving the way for moving SD integrations into a separate discovery package.