.github: add PR template

Author: dbentley-vsql

.github/PULL_REQUEST_TEMPLATE.md

@@ -0,0 +1,18 @@
+## Description
+
+<!-- What does this PR do? Briefly describe the change. -->
+
+## Related Issue
+
+<!-- Link the GitHub issue this PR addresses, e.g. Fixes #123 -->
+
+## How was this tested?
+
+<!-- Describe how you verified your changes. Include test commands you ran. -->
+
+## Checklist
+
+- [ ] I have signed the CLA
+- [ ] I have read [CONTRIBUTING.md](../CONTRIBUTING.md)
+- [ ] I have added or updated tests as appropriate
+- [ ] My changes maintain compatibility with upstream MySQL 8.4