Adds RKE2ControlPlane labels to Machines

[dharmit]

What this PR does / why we need it:
$subject. For details, refer #517.

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 #517

Special notes for your reviewer:

1. This PR has two commits. First one modifies the function signature and requires a change at all places it's called. Second one uses a for loop to make changes only at the place where I think it's reuired. Please suggest which commit to keep of the two.

2. I have tested this using the following manifest:

   manifest

   apiVersion: v1
   kind: Namespace
   metadata:
     name: example-docker
   ---
   apiVersion: cluster.x-k8s.io/v1beta1
   kind: Cluster
   metadata:
     name: rke2-docker
     namespace: example-docker
   spec:
     clusterNetwork:
       pods:
         cidrBlocks:
         - 10.45.0.0/16
       serviceDomain: cluster.local
       services:
         cidrBlocks:
         - 10.46.0.0/16
     controlPlaneRef:
       apiVersion: controlplane.cluster.x-k8s.io/v1beta1
       kind: RKE2ControlPlane
       name: rke2-docker-control-plane
     infrastructureRef:
       apiVersion: infrastructure.cluster.x-k8s.io/v1beta1
       kind: DockerCluster
       name: rke2-docker
   ---
   apiVersion: infrastructure.cluster.x-k8s.io/v1beta1
   kind: DockerCluster
   metadata:
     name: rke2-docker
     namespace: example-docker
   spec:
     loadBalancer:
       customHAProxyConfigTemplateRef:
         name: rke2-docker-lb-config
   ---
   apiVersion: controlplane.cluster.x-k8s.io/v1beta1
   kind: RKE2ControlPlane
   metadata:
     name: rke2-docker-control-plane
     namespace: example-docker
     labels:
       key: value
   spec:
     agentConfig: {}
     machineTemplate:
       infrastructureRef:
         apiVersion: infrastructure.cluster.x-k8s.io/v1beta1
         kind: DockerMachineTemplate
         name: controlplane
       nodeDrainTimeout: 2m
     registrationMethod: control-plane-endpoint
     replicas: 1
     rolloutStrategy:
       rollingUpdate:
         maxSurge: 0
       type: RollingUpdate
     serverConfig:
       disableComponents:
         kubernetesComponents:
         - cloudController
       kubeAPIServer:
         extraArgs:
         - --anonymous-auth=true
     version: v1.30.2+rke2r1
   ---
   apiVersion: infrastructure.cluster.x-k8s.io/v1beta1
   kind: DockerMachineTemplate
   metadata:
     name: controlplane
     namespace: example-docker
   spec:
     template:
       spec:
         bootstrapTimeout: 15m
         customImage: kindest/node:v1.30.0
   ---
   apiVersion: cluster.x-k8s.io/v1beta1
   kind: MachineDeployment
   metadata:
     name: worker-md-0
     namespace: example-docker
   spec:
     clusterName: rke2-docker
     replicas: 1
     selector:
       matchLabels:
         cluster.x-k8s.io/cluster-name: rke2-docker
     template:
       spec:
         bootstrap:
           configRef:
             apiVersion: bootstrap.cluster.x-k8s.io/v1beta1
             kind: RKE2ConfigTemplate
             name: rke2-docker-agent
             namespace: example-docker
         clusterName: rke2-docker
         infrastructureRef:
           apiVersion: infrastructure.cluster.x-k8s.io/v1beta1
           kind: DockerMachineTemplate
           name: worker
           namespace: example-docker
         version: v1.30.2+rke2r1
   ---
   apiVersion: infrastructure.cluster.x-k8s.io/v1beta1
   kind: DockerMachineTemplate
   metadata:
     name: worker
     namespace: example-docker
   spec:
     template:
       spec:
         bootstrapTimeout: 15m
         customImage: kindest/node:v1.30.0
   ---
   apiVersion: bootstrap.cluster.x-k8s.io/v1beta1
   kind: RKE2ConfigTemplate
   metadata:
     name: rke2-docker-agent
     namespace: example-docker
   spec:
     template:
       spec:
         agentConfig: {}
   ---
   apiVersion: v1
   data:
     value: |-
       # generated by kind
       global
         log /dev/log local0
         log /dev/log local1 notice
         daemon
         # limit memory usage to approximately 18 MB
         # (see https://github.com/kubernetes-sigs/kind/pull/3115)
         maxconn 100000
   
       resolvers docker
         nameserver dns 127.0.0.11:53
   
       defaults
         log global
         mode tcp
         option dontlognull
         # TODO: tune these
         timeout connect 5000
         timeout client 50000
         timeout server 50000
         # allow to boot despite dns don't resolve backends
         default-server init-addr none
   
       frontend stats
         mode http
         bind *:8404
         stats enable
         stats uri /stats
         stats refresh 1s
         stats admin if TRUE
   
       frontend control-plane
         bind *:{{ .FrontendControlPlanePort }}
         {{ if .IPv6 -}}
         bind :::{{ .FrontendControlPlanePort }};
         {{- end }}
         default_backend kube-apiservers
   
       backend kube-apiservers
         option httpchk GET /healthz
   
         {{range $server, $backend := .BackendServers}}
         server {{ $server }} {{ JoinHostPort $backend.Address $.BackendControlPlanePort }} check check-ssl verify none resolvers docker resolve-prefer {{ if $.IPv6 -}} ipv6 {{- else -}} ipv4 {{- end }}
         {{- end}}
   
       frontend rke2-join
         bind *:9345
         {{ if .IPv6 -}}
         bind :::9345;
         {{- end }}
         default_backend rke2-servers
   
       backend rke2-servers
         option httpchk GET /v1-rke2/readyz
         http-check expect status 403
         {{range $server, $backend := .BackendServers}}
         server {{ $server }} {{ $backend.Address }}:9345 check check-ssl verify none
         {{- end}}
   kind: ConfigMap
   metadata:
     name: rke2-docker-lb-config
     namespace: example-docker

   And then using below command:

   $ k get machines -o jsonpath='{range .items[*]}{.metadata.labels}' | jq
   {
     "cluster.x-k8s.io/cluster-name": "rke2-docker",
     "cluster.x-k8s.io/control-plane": "",
     "key": "value"
   }

Checklist:

• squashed commits into logical changes
• includes documentation
• adds unit tests
• adds or updates e2e tests

[mjura]

It looks good to me, but linter is yealing

return with no blank line before (nlreturn)

[dharmit]

It looks good to me, but linter is yealing

return with no blank line before (nlreturn)

@mjura I'll remove fix it if we decide to go with the first commit 694170f of this PR. If we choose the second commit, it's going to pass the CI just fine, I tihnk.

[anmazzotti]

Thank you!

[alexander-demicev]

thanks!