Enable the oneof operator for referenced entities

[schustmi]

Describe changes

This PR enables the oneof operator when trying to filter some entity by a referenced entity (e.g. filter pipeline runs by the stack that they were run on).

Pre-requisites

Please ensure you have done the following:

• [ ] I have read the CONTRIBUTING.md document.
• [ ] I have added tests to cover my changes.
• [ ] I have based my new branch on develop and the open PR is targeting develop. If your branch wasn't based on develop read Contribution guide on rebasing branch to develop.
• [ ] IMPORTANT: I made sure that my changes are reflected properly in the following resources:
  • [ ] ZenML Docs
  • [ ] Dashboard: Needs to be communicated to the frontend team.
  • [ ] Templates: Might need adjustments (that are not reflected in the template tests) in case of non-breaking changes and deprecations.
  • [ ] Projects: Depending on the version dependencies, different projects might get affected.

Types of changes

• [ ] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)
• [ ] Other (add details above)