alert_message-1.0.x-dev/alert_message.links.menu.yml

entity.alert_message.settings:
  title: 'Alert message'
  description: 'Configure alert message entity type.'
  route_name:  entity.alert_message.settings
  parent: system.admin_structure
entity.alert_message.collection:
  title: 'Alert messages'
  description: 'List of alert messages.'
  route_name: entity.alert_message.collection
  parent: system.admin_content