Proposal: Describe possible project structure and implications

Initial thoughts around scoping Kubernetes resources to projects and the associated implications.

Intended as a complement to #891, but with more detail on the implementation consequences of project scoping throughout the stack.

Would like to get general agreement on an outline to proceed against to support an initial prototype in next couple weeks.
We should namespace labels, yes, both system-defined labels and user-defined ones. User-defined labels would be implicitly namespaced for the most part, except in operations that span multiple namespaces. In general, my feeling is that we shouldn't go overboard with system-defined labels, but, yes, they should use the namespace of the relevant system component (e.g., identifiers.md proposes a namespace per apiserver).