Cache RA collateral (PCKs, TCB infos) in an on-chain registry

We should cache RA collateral (PCKs, TCB infos, ...) in an on-chain registry in the consensus layer that can be looked up in case Intel services are not available. Most likely this would be a separate consensus service (ra), built in a modular way where Intel SGX is just one of the supported technologies.

The registry should also contain a compact CRL implementation for various keys/certificates used by remote attestation.

The registry should also contain collections of suitable CPUs (by both FMSPC and PPID or similar hardware identifiers to facilitate "proof of cloud" schemes). These collections could be referenced in quote policies for verification instead of specifying individual values. The collections would have administrators that would be allowed to update them (administrators could be vaults to support multisigs or they could be runtimes to allow for custom runtime-defined governance).

Then a PCS client could be built that uses this service as a fallback in case the node's usual PCS endpoint is not available.

Also optimize size of node registration transactions by allowing references to on-chain collateral.