Docs feedback: Dependency Scanning section missing DS_MAJOR_VERSION variable setting

Link the doc and describe what is wrong with it.

Within the Troubleshooting section of Dependency Scanning for Issues building projects with npm or yarn packages relying on Python 2, there's no description of how to use a lower version of retire.js.

Upon further testing I found that adding the DS_MAJOR_VERSION variable, defined within the Dependency-Scanning.gitlab-ci.yml template, to my Project -> Settings -> CI/CD -> Variables, with a value representing a previous version, in this case 2.10.0, allowed the Dependency Scanning job to successfully utilize a previous version of retire.js. It took quite a bit of investigation to determine that all that was needed was to add the DS_MAJOR_VERSION variable to indicate which previous version of retire.js to use.

IMHO, the documentation should capture the DS_MAJOR_VERSION variable within the Available variables section, and call it out in the Issues building projects with npm or yarn packages relying on Python 2 section also.