feat: propose change to the existing PR template

[SamW94]

Description

Propose changes to the existing PR template for the organisation.

Contributors

@SamW94

Type of change

• Refactoring (made code better without changing its behaviour)
• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

How this has been tested

Automated checks will run against this PR.

Checklist

• I have performed a self-review of my code
• I have commented my code in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings

Reviewer Checklist

• I have reviewed the PR and ensured no secret values are present

[github-actions]

Your PR has commits that are missing the Signed-off-by trailer. This is likely due to the pre-commit hook not being configured on your local machine. The usual fix for this issue is to run pre-commit install --install-hooks --overwrite -t commit-msg -t pre-commit, however for more detailed help in setting up the pre-commit hooks, follow the instructions at https://github.com/uktrade/github-standards/blob/main/README.md#usage