chore: add pull request template (#455)

* chore: add pull request template

Adds pull request template to automatically fill out the PR body.

Related to https://linear.app/prefect/issue/PLA-1114/implement-pr-hygiene-improvements

* Mention labels

* Mention title and body reqs

* Mention draft status

.github/pull_request_template.md

@@ -0,0 +1,14 @@
+### Summary
+
+<!-- Add a brief description of your change here -->
+
+### Requirements
+
+- [ ] [Contributing guide](https://github.com/PrefectHQ/prefect-helm/?tab=readme-ov-file#contributing) has been read
+- [ ] Title follows the [conventional commits](https://www.conventionalcommits.org) format
+- [ ] Body includes `Closes <issue>`, if available
+- [ ] Added/modified configuration includes a descriptive comment for documentation generation
+- [ ] Unit tests are added/updated
+- [ ] Deprecation/removal checks are added in `templates/NOTES.txt`
+- [ ] Relevant labels are added
+- [ ] `Draft` status is used until ready for review