Delay generation of costly config elements

[mcculls]

What Does This Do

• Introduce lazy holders to delay computing the (random) runtime-id and hostname until they are needed
• this avoids pulling in various types early, such as ThreadPoolExecutor, meaning fewer weak-context-stores
• Further decoupling of instrumentation related config from the main config to help with native-image

Motivation

When we indirectly pull in types before installing the byte-buddy agent, in this case ThreadPoolExecutor, we lose the chance to add context fields to them. We then have to resort to weak-context-stores which are not as efficient.