EIP-4844: engine_getBlobsBundleV1 specification, extension of engine API

[protolambda]

This is an extension to the Engine API for EIP-4844.

It enables the beacon-node to retrieves the bundle of blobs that is referenced by the blob-transactions in the execution payload.

This is a separate method in a separate document to avoid any collisions with the existing specification while the EIP is a draft and changes may be made.

It is also fully backwards compatible: the method is exposed, but can return an empty list of blobs and kzg commitments for any execution payload without blob transactions.

[protolambda]

Update: force-pushed to extend the word-list to fix the spell check CI, it now includes "ssz", "kzg", and the blobs bundle method name and type

[djrtwo]

nice! I think this is the appropriate structure of the method imo

[timbeiko]

@lightclient @mkalinin we agreed on the 4844 call today we'd like to merge this to have a separate API for blobs for now, and potentially move to having this in getPayloadV2 later. Any objection from either of you?

[lightclient]

Can you rename the file to blob-extension.md or something similar? I don't think we should be using the EIP number as the sole identifier.

[mkalinin]

This change is fine with me as long as it is fine with client developers to keep this version for testing purposes and then potentially switch to getPayloadV2.

For production spec, I would prefer to see blobs information incorporated into getPayloadV2 response as it prevents potential race conditions and reduces testing efforts that would be targeting those race condition scenarios.