Adding a new separate menu link to /admin/config in page?
Adding link to admin config under development, media, service is easy but creating new separate menu like admin_config_development, admin_config_service , admin_config_media is bit tricky. 

As mentioned in


  Create same file with small alteration  modulename.links.menu.yml

modulename.admin_config_modulename:
  title: ' settings'
  description: ' selection.'
  route_name: modulename.settings
  parent: 'system.admin_config'
modulename.second_link:
  title: 'settings'
  description: 'selection.'
  route_name: modulename.settinganother
  parent: 'modulename.admin_config_modulename'  
  menu_name: modulename

  
  By: monkpal