[DOCS]: Pull request template should better enforce issue assignment and focused changes

[KGFCH2]

Problem

The PR template is currently generic and does not emphasize issue assignment or focused scope.

Current Behavior

PRs may be opened without a linked or assigned issue, and reviewers have less guidance.

Why This Improvement Is Needed

A stronger PR template improves contributor discipline and leads to higher-quality, more reviewable pull requests.

Proposed Solution

Update the PR template to add:

• clearer summary guidance
• assignment instructions
• focused change reminders
• a stronger checklist

Expected Outcome

Pull requests become more consistent and easier for maintainers to review.

Additional Notes

This is a documentation-only change.

[github-actions]

Thank you for raising this issue!

We'll review it as soon as possible. We truly appreciate your contributions! ✨

Meanwhile make sure you've visited the README.md, CONTRIBUTING.md, and CODE_OF_CONDUCT.md before creating a PR for this. Also, please do NOT create a PR until this issue has been assigned to you. 😊