add a bit of docs to the add tags tool

[bernt-matthias]

What did you do?

Just add a bit of documentation to the tool and extend test for group tags

• wondering if we want to extend a GTN tutorial on the different tag types and their properties (see Group tags don't propagate #8554 (comment)) I just touched one anyway group tags tutorial improvements training-material#2512

Why did you make this change?

I added a test because I made a mistake while trying this out and thought that adding group tags does not work. So I wanted to see if this works. It does :) .. guess it does not hurt to keep the test anyway.

How to test the changes?

(select the most appropriate option; if the latter, provide steps for testing below)

• I've included appropriate automated tests.
• This is a refactoring of components with existing test coverage.
• Instructions for manual testing are as follows:
  1. [add testing steps and prerequisites here if you didn't write automated tests covering all your changes]

License

• I agree to license these contributions under Galaxy's current license.
• I agree to allow the Galaxy committers to license these and all my past contributions to the core galaxy codebase under the MIT license. If this condition is an issue, uncheck and just let us know why with an e-mail to galaxy-committers@lists.galaxyproject.org.

For UI Components

• I've included a screenshot of the changes

[github-actions]

This PR was merged without a "kind/" label, please correct.