MGMT-19337: enable injection of custom kubelet labels via env var for master nodes

[rccrdpccl]

- What I did
added CUSTOM_KUBELET_LABELS env var to --node-labels parameter for kubelet in master node's template
The use case is a CAPI bootstrap provider install openshift need to advertise a given provider ID via label, so that the infrastructure provider can set the actual provider ID once verified.

- How to verify it
add CUSTOM_KUBELET_LABELS=mydummylabel=myvalue to any of the environmental files used by kubelet (possibly /etc/kubernetes/kubelet-envs)

- Description for the changelog

Inject master node labels via CUSTOM_KUBELET_LABELS env var

[openshift-ci-robot]

@rccrdpccl: This pull request references MGMT-19337 which is a valid jira issue.

Warning: The referenced jira issue has an invalid target version for the target branch this PR targets: expected the story to target the "4.19.0" version, but no target version was set.

In response to this:

- What I did
added CUSTOM_KUBELET_LABELS env var to --node-labels parameter for kubelet in master node's template
The use case is a CAPI bootstrap provider install openshift need to advertise a given provider ID via label, so that the infrastructure provider can set the actual provider ID once verified.

- How to verify it
add CUSTOM_KUBELET_LABELS=mydummylabel=myvalue to any of the environmental files used by kubelet (possibly /etc/kubernetes/kubelet-envs)

- Description for the changelog

Inject master node labels via CUSTOM_KUBELET_LABELS env var

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[openshift-ci]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: rccrdpccl
Once this PR has been reviewed and has the lgtm label, please assign mrunalp for approval. For more information see the Kubernetes Code Review Process.

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[rccrdpccl]

/retest

[rccrdpccl]

/retest

[rccrdpccl]

@umohnani8 could you please take a look 🙏 ?

[rccrdpccl]

/retest

[rccrdpccl]

/retest

[rccrdpccl]

/retest

[openshift-ci]

@rccrdpccl: The following test failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
ci/prow/okd-scos-e2e-aws-ovn	38b0447	link	false	/test okd-scos-e2e-aws-ovn

Full PR test history. Your PR dashboard.

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes-sigs/prow repository. I understand the commands that are listed here.