What is the expected lifecycle of SandboxRuntimeConfig? #1279

This is not new to this PR, so feel free to file an issue and defer, but I wanted to see if you had thoughts in this context first. This addition brings to my attention the question: what is the expected lifecycle of SandboxRuntimeConfig? Some parts, like debug_info and guest_core_dump, seem like they are config of a specific sandbox instance (regardless of what guest/snapshot is being run inside of that instance), while things like entry_point and guest_core_dump seem like they are related fundamentally to the snapshot that's underlying the sandbox, and would need to be reset on restore to have sensible behaviour for a single sandbox that urns multiple different guests at different times.

Originally posted by @syntactically in #1264 (comment)