Add support for Block Acknowledgement from BN to CN

[AlfredoG87]

Currently we are replying the CN with an items_ack, when we receive the block_proof, however we should be returning just a Block Ack once we receive the block_proof but also finish sucessful persistence and verification.

Otherwise BN should return a corresponding Error Message.

1. When CN sends the expected block

   1. Return a PublishStreamResponse
      1. of BlockAcknowledgement with
         1. block_number = received, persisted and verified block number
         2. block_root_hash = block_hash of the received block
         3. block_already_exists = false

2. When CN sends the expected block but fails VERIFICATION

   1. Return a PublishStreamResponse
      1. of EndOfStream with
         1. PublishStreamResponseCode status = STREAM_ITEMS_BAD_STATE_PROOF
         2. block_number = block_number that failed verification