Resource modifier does not allow adding a label

[alfredomagallon]

What steps did you take and what happened:
I tried to use a resource modifier to add a label to a custom resource, in the following way:

patches:
  - operation: add
    path: "/metadata/labels/alfredo"
    value: "true"

However, this is removing all the previous labels present in the resource, and letting the velero added labels only.

What did you expect to happen:

The modifier should have added the label alfredo: "true" to the resource

Environment:

• Velero version:

- Client:
	Version: v1.15.0
	Git commit: -
Server:
	Version: v1.15.0

• Velero features: <NOT SET>
• Kubernetes version (use kubectl version):

Client Version: v1.31.3
Kustomize Version: v5.4.2
Server Version: v1.29.10-eks-7f9249a

• Cloud provider or hardware configuration: AWS EKS
• OS (e.g. from /etc/os-release): Ubuntu

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[ywk253100]

@anshulahuja98 Could you take a look at this?

[anshulahuja98]

Can you try this patch with kubectl once and see if it works as you expect it to?

The design and approach is inspired from [kubectl patch command](https://github.com/kubernetes/kubectl/blob/0a61782351a027411b8b45b1443ec3dceddef421/pkg/cmd/patch/patch.go#L102C2-L104C1)
Update a container’s image using a json patch with positional arrays kubectl patch pod valid-pod -type='json’ -p=’[{“op”: “replace”, “path”: “/spec/containers/0/image”, “value”:“new image”}]’
Before creating the resource modifier yaml, you can try it out using kubectl patch command. The same commands should work as it is.