Detect & handle LICENSES folder with multiple files

Problem to solve

If a project consists of content for which multiple license files need to be provided, reuse.software/spec prescribes a LICENSES folder. For example: (scientific) projects with data as CC0, text & figures as CC-BY..., and analysis code with any software license.

GitLab's LICENSE button on a project's overview page currently does not detect this situation, see demo: katrinleinweber/gitlab-ee (diff).

Intended users

Rachel (Release Manager) when QA-ing a public release
Dana (Data Analyst) when preparing a project for publication

Further details

Proposal

License detection might need to be upgraded to detect LICENSES folder and/or file as well.
Maybe the current LICENSE button could become a drop-down menu with 1 entry for each file found in a LICENSES folder.

Permissions and Security

Documentation

Availability & Testing

What does success look like, and how can we measure that?

Fewer "LICENSE" did not exist on "master" flash-notices, if those are being logged.

What is the type of buyer?

Links / references

#2592 (comment 51300870)