[MEV-Boost\builder] implement execution builder api client

[tbenr]

PR Description

• Introduces Web3JExecutionBuilderClient
• Introduces all the required execution client schema files to support the new apis
• Introduced required SSZ objects (SignedValidatorRegistrationV1 and SignedBuilderBidV1) to be able to handle the signature (generation\validation).

In upcoming PR I'll remove builder API from Web3JExecutionEngineClient and integrate Web3JExecutionBuilderClient in ExecutionEngineChannel

Fixed Issue(s)

related to #5396

Documentation

• I thought about documentation and added the doc-change-required label to this PR if updates are required.

Changelog

• I thought about adding a changelog entry, and added one if I deemed necessary.

[ajsutton]

Worth talking through the details of this on the call tonight - I think it generally looks right, but I am quite confused why the execution builder is returning beacon block content like slashings etc. The execution layer ideally wouldn't know anything about those and that's where most of the API trouble is coming from. But I'm not familiar with the latest builder api specs so am probably missing something.

And I think there's a strong argument here that we should be able to have a version of these APIs that does just send SSZ instead of JSON - particularly if the whole beacon block winds up needing to be sent.

[lightclient]

I am quite confused why the execution builder is returning beacon block content like slashings etc. The execution layer ideally wouldn't know anything about those and that's where most of the API trouble is coming from.

@ajsutton the builder is accepting beacon block content, not returning it. They need the signed blinded beacon block to verify the proposer's signature and to be able to release it the network in case the proposer tries to withhold. If they only received the blinded beacon block header, they wouldn't have enough information to propagate the block on their own.