PoC support for dedicated apm agent attacher integration

@eyalkoren is going to research what is necessary for building a dedicated apm agent attacher integration and prototype it. This task is about supporting this effort with knowledge and help building some tooling on request.

Initially we will collect and provide information about requirements for building an Elastic Agent (&Fleet) integration. But this task also includes help building some test automation and tooling for building and packaging the integration, and general golang support and reviews.