docs: add a pull request template (#22063)

.github/pull_request_template.md

@@ -0,0 +1,11 @@
+## Check List
+
+<!-- Please check the list. Please don't remove the check list. -->
+
+- [ ] Read [CONTRIBUTING.md](https://aquaproj.github.io/docs/products/aqua-registry/contributing)
+  - [ ] Read [OSS Contribution Guide](https://github.com/suzuki-shunsuke/oss-contribution-guide/blob/main/README.md)
+- [ ] [All commits are signed](https://docs.github.com/en/authentication/managing-commit-signature-verification/signing-commits)
+- [ ] [Avoid force push](https://github.com/suzuki-shunsuke/oss-contribution-guide?tab=readme-ov-file#dont-do-force-pushes-after-opening-pull-requests)
+- [ ] Do only one thing in one Pull Request
+
+<!-- Please write the description here -->