feat(api): Add new destinations pipelines delete endpoint and rework constraints

[iambriccardo]

This PR introduces a new endpoint that atomically deletes both a destination and its associated pipeline. It also includes the following improvements:

• Ensures that the replicator entry is deleted when its corresponding pipeline is removed. This is done assuming that there can be a single replicator bound per pipeline.
• Removes ON DELETE CASCADE constraints for sources and destinations. Instead, the system now explicitly throws an error if a source or destination with active pipelines is deleted. This makes deletion behavior more predictable and explicit.