I am trying to add programmaticaly a custom,parent panel to the admin/config menu, so i can add other links to it, config pages of other modules etc. How can that be done? I am able to add custom module, under admin/config/development/my_module, for example, but i would like to group all my modules under same, custom parent panel.
Check in contrib modules for examples. Example from message module - message.links.menu.yml
message.overview_templates:
title: 'Message templates'
parent: system.admin_structure
description: 'Manage message templates.'
route_name: message.overview_templates
message.main_settings:
title: 'Message'
route_name: message.main_settings
parent: system.admin_config
description: 'Tools that enhance the user interface.'
weight: -10
message.settings:
title: 'Message'
description: 'Message settings.'
parent: 'message.main_settings'
route_name: message.settings
Also, check the official documentation: https://www.drupal.org/docs/8/creating-custom-modules/add-a-menu-link