chore(github): update PR template.

[KevinMind]

trafficstars

Thanks for opening a Pull Request (PR), here's a few guidelines as to what we need in your PR before we review it.

Fixes: N/A

How did you solve the problem?

I updated the github PR template to include specific sections for required information and clear descriptions. Each section includes examples and links to help the PR author and specifies which sections are required.

What should the reviewer focus on?

If we want to maintain a separate pull request template for community PRs, that is also possible. We can create a directory of PR templates and open them with query parameters or selecting in the Web UI.

If we want to extend this template to other addon repositories, we could do so, but would require moving the addon repos to a separate org. Probably not worth it.

How to test this PR?

No testing required.

[diox]

Note: we should consider adding "Fixes mozilla/addons#xxx" to the template to make transition to new unified new issue (which go to mozilla/addons) template