[DECOUPLING] Implement BlobSidecarsByRoot RPC method

[mehdi-aouadi]

BlobSidecarByRoot v1
Protocol ID: /eth2/beacon_chain/req/blobs_sidecar_by_root/1/

Request Content:

class BlobSidecarRequest(Container):
    beacon_block_root: Root
    blob_index: uint64
    
(
  List[BlobSidecarRequest, MAX_REQUEST_BLOCKS]
)
Response Content:

(
  List[BlobSidecar, MAX_REQUEST_BLOCKS]
)