feat: allow setting custom parents via metadata (Alpha) #5082

[jake-ciolek]

I took a stab at #5082 and took a slightly different approach. Instead of users specifying the parent/child relationship in config, we could allow setting it in the metadata.

This change allows users to define a parent/child relationship for resources where this cannot be inferred from the ownerRef values. The child resource might be a Cluster-scoped CR and the parent might be a namespaced CRD.

The API is straightforward and boils down to setting annotations that define the parent, i.e:

argocd.argoproj.io/ownerApiVersion: custom-api.example.com/v1alpha1
argocd.argoproj.io/ownerKind: Database
argocd.argoproj.io/ownerName: my-claimed-database
argocd.argoproj.io/ownerNamespace: parent-namespace

If a custom parent is defined, we take it over the ownerRef values.

This allows us to display a more ordered resource tree. Some concrete examples include Istio Operator and Crossplane resources (relationship between Claims and Composite Resources).

In the screenshots, you can see that it brings order to the resource tree of Istio Operator and draws the relationship between Crossplane Claim and Crossplane XR.

This is an early implementation and I would appreciate feedback on this approach and pointers on how to make it better. Thanks!

Updates #5082

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[andrii-korotkov-verkada]

Do you have a gitops-engine PR to update the tree construction logic?

[reggie-k]

Thanks for the PR!
Maybe the annotations should be called "argocd.argoproj.io/parentName", "parentKind", etc, since they are referred to as parents in other parts of the code?
And could you add docs for this in the docs/user-guide/annotations-and-labels.md?