[Temporary] Allow Heterogeneous Aggregates - Do Not Merge

[matheusfm]

Description

This is a temporary PR to deploy a preview version and demonstrate how to allow heterogeneous aggregates with CEL.

Please do not merge this PR.

Linked Issues

https://github.com/undistro/cel-playground/issues/98

Checklist

• [ ] I have labeled this PR with the relevant Type labels
• [ ] I have documented my code (if applicable)
• [x] My changes are covered by tests