ci: pull request template

[d0choa]

✨ Context

As discussed in @RobinM-code in #510, we would benefit from having a PR template so that contributors understand what are the expectations when opening new PRs.

🛠 What does this PR implement

A Github PR template.

🙈 Missing

Templates are a very subjective topic. I welcome any feedback you might have cc @RobinM-code @DSuveges @ireneisdoomed

🚦 Checks

• covers one single feature (one change at a time)
• documentation added/updated
• there is no commented out code in this PR
• follows conventional commits in PR title and commits.
• is up-to-date with dev branch
• tests have been added to verify that the new code works
• passes local tests (make test)
• passes pre-commits (e.g poetry run pre-commit run --all-files)

[ireneisdoomed]

Thank you! I have stylistic suggestions, based on the Transformers PR template
Currently our contribution guidelines are "polluted" with instructions about environment set up, we could improve this.

[ireneisdoomed]

Suggested change

	<!--- What's the context for the changes? If the changes are related to a specific issue, please [link](https://docs.github.com/en/issues/tracking-your-work-with-issues/linking-a-pull-request-to-an-issue) to it:_
	<!---
	Congratulations! You've made it this far!
	Once merged, your PR is going to appear in the release notes with the title you set, so make sure it's a great title that fully reflects the extent of your contribution.
	What's the context for the changes? If the changes are related to a specific issue, please [link](https://docs.github.com/en/issues/tracking-your-work-with-issues/linking-a-pull-request-to-an-issue) to it:_

[RobinM-code]

Some nice work @d0choa, this will help for sure!

Also:

Currently our contribution guidelines are "polluted" with instructions about environment set up, we could improve this.

Agree with this :)

[DSuveges]

I think these are fine, if changes will be necessary later, it can always be updated.

[ireneisdoomed]

Ty for the changes!