chore(github): add default pull request template

.github/PULL_REQUEST_TEMPLATE/pull_request_template.md

@@ -0,0 +1,23 @@
+<!-- Please make sure your commit messages follow Conventional Commits
+(https://www.conventionalcommits.org) with a commit type (e.g. feat, fix, refactor, chore):
+
+Bad:        Added support for release links
+Good:     feat(api): add support for release links
+
+Bad:        Update documentation for projects
+Good:     docs(projects): update example for saving project attributes-->
+
+## Changes
+
+<!-- Remove this comment and describe your changes here. -->
+
+### Documentation and testing
+
+Please consider whether this PR needs documentation and tests. **This is not required**, but highly appreciated:
+
+- [ ] Documentation in the matching [docs section](https://github.com/python-gitlab/python-gitlab/tree/main/docs)
+- [ ] [Unit tests](https://github.com/python-gitlab/python-gitlab/tree/main/tests/unit) and/or [functional tests](https://github.com/python-gitlab/python-gitlab/tree/main/tests/functional)
+
+<!--
+Note: In some cases, basic functional tests may be easier to add, as they do not require adding mocked GitLab responses.
+-->