chore(ci): Use release-please to orchestrate releases

[Tom-Owen-ONS]

📌 Pull Request Template

Please complete all sections

✨ Summary

This PR simplifies the release process to use the release-please tool for automated CHANGELOG management and release versioning. To do a release, simply merge the automated PR that is generated into main.

📜 Changes Introduced

• Feature implementation (feat:) / bug fix (fix:) / refactoring (chore:) / documentation (docs:) / testing (test:)
• Updates to tests and/or documentation
• Terraform changes (if applicable)

✅ Checklist

Please confirm you've completed these checks before requesting a review.

• Code passes linting with Ruff
• Security checks pass using Bandit
• API and Unit tests are written and pass using pytest
• Terraform files (if applicable) follow best practices and have been validated (terraform fmt & terraform validate)
• DocStrings follow Google-style and are added as per Pylint recommendations
• Documentation has been updated if needed

🔍 How to Test

If you like, I can add this branch to the triggers so that you can see what the resulting PR would look like.