Implement Feature for Adding New Signatories via Client CLI

[AlexStroke]

Objective:

We need to extend the functionality of our iroha_client_cli to allow users to add new signatories to existing accounts.

Requirements:

• Suggested command format:

  ./iroha_client_cli account add-signatory \
      --account_id="<account_id>" \
      --public_key="<new_public_key>"
  

• Where account_id is the ID of the account to which the signatory is being added, and public_key is the public key of the new signatory.

[s8sato]

• blocked by #4373

may become obsolete after #4373 as signatories are planned to be immutable so far