🐛 topology: use raw input object for patch calculation in WalkTemplates

[chrischdi]

What this PR does / why we need it:

This PR adjusts the WalkTemplates function provided for runtime extensions to use the original input struct to calculate patches.

Before it did use the typed objects to marshal them and create the patch.
This could lead to invalid patches because the Go struct may have fields which the original input did not have.

Example for VSphereClusterTemplate from here: https://github.com/kubernetes-sigs/cluster-api-provider-vsphere/blob/main/apis/v1beta1/vsphereclustertemplate_types.go#L33

Consider the following input from the patch request (the template referred by the ClusterClass):

{
  "apiVersion": "vmware.infrastructure.cluster.x-k8s.io/v1beta1",
  "kind": "VSphereClusterTemplate",
  "metadata": {
    "name": "quick-start-supervisor",
    "namespace": "k8s-upgrade-with-runtimesdk-csmelk",
  },
  "spec": {
    "template": {
      "spec": {}
    }
  }
}

decoding and marshalling again made the following out of it:

{
  "apiVersion": "vmware.infrastructure.cluster.x-k8s.io/v1beta1",
  "kind": "VSphereClusterTemplate",
  "metadata": {
    "name": "quick-start-supervisor",
    "namespace": "k8s-upgrade-with-runtimesdk-csmelk",
  },
  "spec": {
    "template": {
      "spec": {
        "controlPlaneEndpoint": {
          "host": "",
          "port": 0
        }
      }
    }
  }
}

Now we calculate the patch based on the following:

{
  "apiVersion": "vmware.infrastructure.cluster.x-k8s.io/v1beta1",
  "kind": "VSphereClusterTemplate",
  "metadata": {
    "name": "quick-start-supervisor",
    "namespace": "k8s-upgrade-with-runtimesdk-csmelk",
  },
  "spec": {
    "template": {
      "spec": {
        "controlPlaneEndpoint": {
          "host": "1.1.1.1",
          "port": 6443
        }
      }
    }
  }
}

The old behaviour would have created the following patch:

[
  {
    "op": "replace",
    "path": "/spec/template/spec/controlPlaneEndpoint/host",
    "value": "1.1.1.1"
  },
  {
    "op": "replace",
    "path": "/spec/template/spec/controlPlaneEndpoint/port",
    "value": 30000
  }
]

This patch would fail in CAPI to get applied to the template with following error:

error computing the desired state of the Cluster topology: failed to apply patches: failed to apply patches for patch "test-patch": failed to apply patch: error applying json patch (RFC6902): replace operation does not apply: do
c is missing path: /spec/template/spec/controlPlaneEndpoint/host: missing value

The new behaviour would create the following patch, which would work:

[
  {
    "op": "add",
    "path": "/spec/template/spec/controlPlaneEndpoint",
    "value": {
      "host": "1.1.1.1",
      "port": 6443
    },
  }
]

Which issue(s) this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close the issue(s) when PR gets merged):
Fixes #

/area runtime-sdk

[chrischdi]

/assign @fabriziopandini @sbueringer

[chrischdi]

/test help

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[chrischdi]

/test pull-cluster-api-e2e-main

[sbueringer]

Thx!

/lgtm
/approve

[k8s-ci-robot]

LGTM label has been added.

Git tree hash: 75cb9509c476eb5d2eeb995bd88f830866b838ce

[k8s-ci-robot]

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