Create GitHub Action to Email Developers on DDL Change

### Task Summary

To communicate SQL DDL changes to all developers, we want to create a GitHub action to email developers whenever a PR with the label `ddl-change` is merged. 

### Priority

P2 – Medium

### Task Type

- [ ] Code Implementation
- [ ] Documentation
- [ ] Refactor / Cleanup
- [ ] Testing / QA
- [x] DevOps / Deployment