Turn "preserve-unknown-fields" into serde_json::Value for more cases

[felipesere]

While converting a FluxV2 Kustomization CRD into Rust I hit these cases of x-kubernetes-preserve-unknown-fields.

[clux]

hey, thanks a lot for fixing this, this is a great starting point for one of the many cases mentioned in #31

I am happy to merge this as is, but I am thinking we should probably change the default thing to use here should really be a HashMap<String, Value> rather than a Value direct for reasons outlined in kube-rs/kube#844

[clux]

This definitely fixes parts of the flux crds which gave the following error

$ kopium kustomizations.kustomize.toolkit.fluxcd.io
Error: unsupported recursive array type for patchesStrategicMerge

where

              patchesStrategicMerge:
                description: Strategic merge patches, defined as inline YAML objects.
                items:
                  x-kubernetes-preserve-unknown-fields: true
                type: array

was part of the schema.

can see that this is meant to be a vector of some arbitrary data as per their docs:

        patchesStrategicMerge:
          - kind: Deployment
            apiVersion: apps/v1
            metadata:
              name: metrics-server
            spec:
              template:
                spec:
                  tolerations:
                    - key: "workload-type"
                      operator: "Equal"
                      value: "cluster-services"
                      effect: "NoSchedule"

and we are now (with this change) generating:

pub patchesStrategicMerge: Option<Vec<serde_json::Value>>

i think this should be generated as Option<Vec<HashMap<String, Value>>> rather than what we currently have since it's an array which has the items key implying a vec of objects.

Going to merge this and clean it up with a test case for a flux crd.
Thanks a lot for this.