The plugin has no license #179

Summary

Add a LICENSE file to license the code under a suitable open source license.

Detailed description

I noticed while setting up some testing that compose_plugin doesn't have a license. There's no LICENSE file, GitHub doesn't detect one for this repository or for dcflachs/compose_plugin it was forked from, and the README's License section only says "This project is open source. See the repository for license details." The one license line in the repository is "license": "MIT" in composer.json.

Without a license, nobody strictly has permission to use, copy, modify or redistribute the code, however open the intent is. It also blocks tools whose terms only cover licensed open source code. Claude refuses to setup the CodeQL command-line tool to run tests like GitHub does, because it may only be used on a codebase "released under an OSI-approved License", so I can't as easily run the same scan locally that runs on PRs here.

I don't think this is easy to fix, because most of the original code is dcflachs's, and dcflachs/compose_plugin is archived and unlicensed too. I think (I'm not a lawyer) you can put a license on your own work and on contributions from here on, but the original code needs dcflachs's agreement. A few people contributed to the original as well.

Some options:

1. Reach dcflachs, on the Unraid forum maybe, and ask whether the original can be released under a license (MIT would match composer.json). If they agree, add a LICENSE file here.
2. Meanwhile, add a LICENSE that covers your changes and new contributions, with a note that code from dcflachs/compose_plugin is not covered until dcflachs agrees.
3. Add a line to the README or CONTRIBUTING saying contributions are accepted under that license, so new code doesn't add to the problem.

Alternatives considered

No response