How do I create a configuration menu with the selected section name? I want to create a menu in the admin section that is in the sitename/admin/config path.

As of now, I am doing this. 

Routing file

custom_menu.adminmenu_section:
    path: '/admin/config/custommenu'
    defaults:
        _controller: 'Drupal\custom_menu\Controller\CustomMenuController::content'
        _title: 'Custom Menu Configuration'
    requirements:
        _permission: 'administer site configuration'

custom_menu.admin_menu:
    path: '/admin/config/custommenu/customconf'
    defaults:
        _form: 'Drupal\custom_menu\Form\CustomMenuForm'
        _title: Custom Menu creation
    requirements:
        _permission: 'administer site configuration'


links.menu file

custom_menu.adminmenu_section:
    title: 'Configuration'
    description: 'Custom Menus Configuration section'    
    parent: system.admin
    route_name: custom_menu.adminmenu_section

custom_menu.admin_menu:
    title: 'Custom Menus Conf'
    description: 'Custom Menus Configuration section'
    parent: custom_menu.adminmenu_section
    route_name: custom_menu.admin_menu


This code is not creating a section in the admin/config path. But when I used  parent: system.admin_config that time I will get menu in the admin section but the section name will be CONFIGURATION. Because its title given in the system.admin_config route, but I don't want that name.

I want to create a section with separate name. How can I achieve that?
I tested it with your code and you just have to change two little things in your custom_menu.adminmenu_section. The rest is ok. See below:

module.links.menu.yml

custom_menu.adminmenu_section:
  title: 'Configuration' &lt;= change this to your section name
  description: 'Custom Menus Configuration section'    
  parent: system.admin_config  &lt;= change this to system.admin_config
  route_name: custom_menu.adminmenu_section