chore(github): replace PR guidelines checkbox with reminder text

[ljanner]

Replace contribution guidelines checkbox in PR template

The contribution guidelines checkbox in the PR template has become a low-signal step for regular contributors and adds noise to every PR body.

For new contributors, a reminder can still be useful during PR creation.

Three options:

Option 1: 🎉 Remove checkbox

Please make sure your PR follows the [contribution guidelines](https://github.com/siemens/element/blob/main/CONTRIBUTING.md).

Option 2: 🚀 HTML comment

As the reminder doesn't serve a purpose in the description but rather when creating we could make it an HTML comment that is then hidden once created. Although a mardown link does not work in this case, so it would be like this:

<!-- Please make sure your PR follows the contribution guidelines. -->

Option 3: 👀 Remove it entirely

[gemini-code-assist]

Code Review

This pull request replaces the contribution guidelines checkbox in the PR template with a line of text, which is a good change to reduce noise in pull request bodies. The suggestion to use an HTML comment to further improve this by making the reminder visible during PR creation but hidden from the final PR description is retained, as it aligns with the goal of reducing noise and does not contradict any provided rules.

[ljanner]

I'd like to start a little vote here about this topic. PR is currently in draft to avoid accidental merge.

As I'm unavailable for the core-team meeting I would greatly appreciate if someone could potentially take over the discussion lead here if we don't already find a common solution through voting. If you have other ideas or further suggestions to the PR template I'm happy to hear suggestions 😄

@siemens/siemens-element-members @siemens/siemens-element-owners

[github-actions]

[github-actions]

Documentation.
Examples.
Playwright report.

Coverage Reports:

• element-ng
• element-translate-ng