Add KubeVirt platform type

[nirarg]

This is the first PR adding KubeVirt provider to Openshift.
Please find the related enhancement for this change:
openshift/enhancements#417

In addition to this repository, there are also changes in repositories (WIP):

• openshift/installer (https://github.com/nirarg/installer/tree/kubevirt-provider)
• openshift/machine-api-operator (https://github.com/nirarg/machine-api-operator/tree/kubevirt-provider)
• openshift/cloud-credential-operator (https://github.com/bardielle/cloud-credential-operator)
• openshift/machine-config-operator (https://github.com/ravidbro/machine-config-operator/tree/add_ocp_platform)

Also added new repository for machine-api-operator access the new provider (WIP):

• https://github.com/ravidbro/cluster-api-provider-kubevirt

[nirarg]

/test verify

[nirarg]

/assign @knobunc

[knobunc]

/lgtm

[openshift-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: knobunc, nirarg

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[rgolangh]

@knobunc @deads2k this PR is not going to be downported to release-4.6 - do we still need to open a bugzilla for that?