Produce a new blinded block, without signature.

get https://{server_url}/{api_key}/eth/v1/validator/blinded_blocks/{slot}

Requests a beacon node to produce a valid blinded block, which can then be signed by a validator.
A blinded block is a block with only a transactions root, rather than a full transactions list.

Metadata in the response indicates the type of block produced, and the supported types of block
will be added to as forks progress.

Pre-Bellatrix, this endpoint will return a BeaconBlock.