Blob retrieval by versioned hash

Currently, in the construction of retrieving a blob, the request is based on the block ID, which can be either a block root or specific keywords like "finalized" or "justified." However, it would be beneficial for L2 in general to have the ability to retrieve blobs using versioned hashes. This would address a pain point for L2 mapping, as L2s primarily focus on versioned hashes and it would be more sensible to use them as the request parameter rather than beacon block roots

Start by reviewing the blob-retrieval API definition and how its request currently accepts a block ID, including the supported block-root keywords. Done means the API specification clearly supports versioned hashes as a retrieval parameter and explains the expected behavior for that form.

Written by the indexing model from the issue text.