code: def subdomains_init(blockstack_opts, working_dir, atlas_state):
      
      if not is_subdomains_enabled(blockstack_opts):
          return None
  
      subdomain_state = SubdomainIndex(blockstack_opts['subdomaindb_path'], blockstack_opts=blockstack_opts)
      atlas_node_add_callback(atlas_state, 'store_zonefile', subdomain_state.enqueue_zonefile)
  
      return subdomain_state
docs: Set up subdomain state
      Returns a SubdomainIndex object that has been successfully connected to Atlas