Change templates for pull requests and submitting issues.

[shibatch]

Checklist

• I have read the contributing guidelines.
• I have considered portability of my change across platforms and architectures.
• I have self-reviewed my code.
• I have commented my code where necessary.
• I have updated the documentation accordingly.
• I have added tests that prove my fix is effective or that my feature works.

What is the purpose of this pull request?

• Fix a bug
• Improve code quality or performance
• Add support for a new vector extension
• Add a workflow to GitHub Actions or add/modify a job in an existing workflow
• Documentation update
• Other, please explain:

What changes did you make?

This PR consists in...

Does this PR relate to any existing issue?

Relates to/Fixes # (issue)

Is there anything you would like reviewers to focus on?

Please on focus on...