component_guide: Update import-debian-package documentation

Task: https://phabricator.apertis.org/T8106

import-debian-package script now runs all the steps automatatically. The recently added --push-remote option allows creating and pushing the imported package to apertis remote gitlab instance.

The following steps are now automatized:

• package folder is created and import process is performed in there.
• remote repo is created if it doesn't exist.
• remote branches and tags are pushed.
• gitlab settings are applied to remote repo.
• CI pipeline is triggered on all downstream branches.

The previously manual steps (performed now by the script) are kept documented in the import-debian-package repository.