refactor: move DependencyReference to apis/meta

[vecil]

Extract DependencyReference to apis/meta (Fix #1034)

Summary

This PR moves the duplicated DependencyReference type from controller-specific APIs into apis/meta to provide a single shared implementation across Flux components.

Changes

• Added DependencyReference to apis/meta
• Updated ObjectWithDependencies to use []DependencyReference
• Added MakeDependsOn helper with CEL (@expr) support
• Updated dependency sorting logic and tests accordingly
• Added deepcopy implementations for the new type

Motivation

DependencyReference was duplicated across KC and HC APIs. Centralizing it in apis/meta removes duplication and enables consistent dependency handling, including CEL-based readiness expressions used by the Flux CLI.

Notes

• Backward behavior preserved.
• Follow-up update will be required in fluxcd/flux2 to use the shared type in utils.MakeDependsOn.
• Follow-up update will be required in fluxcd/kustomize-controller and fluxcd/helm-controller to use the shared type in meta.DependencyReference.
• Cherry-picked from refactor: move DependencyReference to apis/meta #1129, thank you very much @Iam-Karan-Suresh 🚀