Create and use generic send_doc_confirmation()

• Create generic send_doc_confirmation()
• Use it in send-document commands
  • certify
  • membership
  • transfer v2
  • other cmds
• Adapt tx tests
• Create patched_send_doc_confirmation()

#379: Would allow to run test_membership_cmd() without sending the document by running patched_send_doc_confirmation.assert_awaited_once_with()