Decide how to license compose-tests #78

This repo doesn't have a license yet, and it's the trickiest one in our org-wide license review because most of it is inherited.

About 770 of the roughly 830 files are in tests/legacy/, imported from the CentOS t_functional suite in November 2023. t_functional has no repository-wide license. Some of those files carry GPL-2.0-or-later or GPL-3.0-or-later headers, and many carry no notice at all, so we can't relicense them.

The rest of the repo is original tmt tests and plans. The repo was created in 2024, after the AlmaLinux OS licensing policy added its guidance that unique software that doesn't ship in the OS should use GPLv3.

Our best guess is in a draft PR (linked below): GPL-3.0-or-later for the repo, plus a README note that tests/legacy/ keeps its original per-file terms. Both GPL-2.0-or-later and GPL-3.0-or-later files are compatible with that.

Does this match how you think about the legacy tests? Is anything in tests/legacy/ something we should treat differently?

Part of the org-wide license review in AlmaLinux/.github#7.