Builder flow for Deneb / Blobs

[jimmygchen]

Issue Addressed

#3689

Builder spec: ethereum/builder-specs#61
4844 Builder flow: https://hackmd.io/@jimmygchen/B1dLR74Io

Proposed Changes

Beacon Node

• produceBlindedBlock endpoint updates
  • Handle new Deneb BuilderBid response from builder endpoint (new BlindedBlobsBundle type)
  • Build BlockContents response (containing kzg_commitments, proof and blinded_blob_sidecars)
• submitBlindedBlock endpoint updates
  • Handle SignedBlockContents request and forward to builder
  • Handle unblinded ExecutionPayloadAndBlobsBundle response from builder endpoint, and publish block

Validator Client

• Handle produceBlindedBlock response from Beacon API
• Individual signing of blinded_blob_sidecars
• Build SignedBlockContents and submit to Beacon API (submitBlindedBlock)

Task List

• Cleanup: move types under deneb_types to their respective files.

[jimmygchen]

There are some issues with my first attempt - code duplication & enum wrappers for blobs / blinded blobs were making things a bit messy and difficult to progress further - so I've started over again using generics instead, similar to how we implemented it for Payload in BeaconBlockBody and it seems a bit cleaner. New branch here: https://github.com/jimmygchen/lighthouse/tree/deneb-builder-take-2

I'll switch the PR to the new branch once I've moved everything I need over to that branch.

[jimmygchen]

Closing in favour of #4428