simplify our GH issue templates boilerplate

### New feature, improvement proposal

reporting here as is it a general topic for many Git repositories, even if [templates in this precise Git repo](https://github.com/apache/maven-gh-actions-shared/tree/main/.github/ISSUE_TEMPLATE) do not suffer from reported need

we have created issue templates that contain a lot of boilerplate: this was ok when we used Jira, with its Jira issue description that explained the intent, then the PR were "just" an implementation
Nowadays, the GH issue is the only tracking item: its first comment = the description, is key for tracking the intent, any boilerplate at that level is just lowering signal to noise ratio

see for example https://github.com/apache/maven-site/pull/787 (just picking one random case)
many people don't even get that the checkboxes inserted are to be used: and Maven committers honestly do not check if they were used before merging
I personally simply drop the boilerplate for my own PRs: useless noise

it would be useful to simplify to ease understanding

ideas:
- instead of template that adds boilerplate to the first comment, do some GHA to have that boilerplate as a separate comment
- use a bot for license checks (that also tracks as secondary comments)

Start by reviewing the templates under .github/ISSUE_TEMPLATE and the linked maven-site pull request for the boilerplate this issue discusses. The next step is to establish whether the project wants simpler templates, separate automated comments, or bot-based license checks; done criteria are not defined beyond reducing boilerplate and preserving useful tracking information.

Written by the indexing model from the issue text.