Enhanced Scalability for Verifier and Registrar

# Enhancement Description
Enhanced Scalability for Verifier and Registrar
- Keylime Enhancement Proposal: TBD
- Primary contact (assignee): @mpeters
- Enhancement target (which target equals to which milestone):
- Alpha release target: TBD
- Beta release target: TBD
- Stable release target: TBD

There are currently experiments ongoing that have keylime verifying 2000+ nodes at a basic level. Take the lessons learned from these experiments and design an enhanced Scalability and High-Available design for internal keylime components as well as good documentation for how to scale it. We also want to expand beyond the basic verifications being tested and perform full allow-list verification on each node. The goal is to achieve at least a reasonable level of horizontal scalability.