chore: add preview and testing and notes section to pr template

[zimeg]

Changelog

N/A - But we hope to improve PRs onward!

Summary

This PR adds the "preview" and "testing" and "notes" section to PR templates as placeholders for more detailed changes.

Notes

Multiple templates were considered but AFAICT a good solution for selecting these doesn't exist. IMHO removing unneeded sections is easier than adding these?

• GitHub Docs: https://docs.github.com/en/communities/using-templates-to-encourage-useful-issues-and-pull-requests/creating-a-pull-request-template-for-your-repository
• GitHub Docs: https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/proposing-changes-to-your-work-with-pull-requests/using-query-parameters-to-create-a-pull-request
• Stack Overflow: https://stackoverflow.com/questions/73771068/multiple-templates-for-pull-requests-on-github

Requirements

• I've read and understood the Contributing Guidelines and have done my best effort to follow them.
• I've read and agree to the Code of Conduct.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 71.21%. Comparing base (346be01) to head (04c2914).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #489   +/-   ##
=======================================
  Coverage   71.21%   71.21%           
=======================================
  Files         222      222           
  Lines       18664    18664           
=======================================
  Hits        13292    13292           
  Misses       4190     4190           
  Partials     1182     1182           

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