Removing need for new_problem.yaml to avoid ugly failing on default

[CIGbalance]

This pull request updates the workflow for checking new problem submissions and improves related documentation and configuration. The main changes are focused on making the workflow more robust and providing better examples for contributors.

Workflow improvements:

• The GitHub Actions workflow (.github/workflows/new_problem_check.yml) now only runs on pushes to the main branch / pull requests and only if utils/new_problem.yaml has changed, reducing unnecessary workflow runs.
• The workflow step to run the new problem check now only executes if utils/new_problem.yaml exists, preventing errors when the file is missing.

Documentation and configuration updates:

• Added a new problem example to utils/README.md to help contributors format their submissions correctly.
• Removed the template entry from utils/new_problem.yaml to keep the configuration clean and avoid accidental submissions of the template.

[Copilot]

Pull request overview

This PR aims to make the “new problem” submission check more robust by avoiding failures when utils/new_problem.yaml is missing, while also updating contributor guidance and cleaning up the template configuration.

Changes:

• Adjust GitHub Actions triggers/conditions for the new-problem validation workflow.
• Add a “new problem” example to utils/README.md.
• Remove the template entry from utils/new_problem.yaml (file is now removed in this branch).

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 4 comments.

File	Description
utils/README.md	Adds an example snippet for contributors submitting new problems.
utils/new_problem.yaml	Removes the template content (file no longer present after the change).
.github/workflows/new_problem_check.yml	Limits push triggering to main and skips the validation step if utils/new_problem.yaml is absent.

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[kvdblom]

Some small things, main thing is to update the instructions. There are also the AI comments, some appear like they might make sense.

[kvdblom]

The :alert: tags don't seem to render when previewing this: https://github.com/OpenOptimizationOrg/OPL/blob/3535ab500a7863081cb8e35bd7933bed6197939a/utils/README.md

[CIGbalance]

Fixed!

[kvdblom]

Should these instructions change now that the file is removed? Explain that they have to create it from the example below?

[CIGbalance]

Done!