Add SELinuxMount feature gate

[jsafrane]

Add a new feature gate SELinuxMount that configures AWS EBS CSI driver installed by kOps for SELinuxMount support.

• It projects necessary SELinux /etc and /sys directories from the host to the CSI driver (see KEP for details)
• It sets CSIDriver.Spec.SELinuxMount: true

I added KopsFeatureEnabled function to templates to have a nice {{ if KopsFeatureEnabled "SELinuxMount" }} there.

[hakman]

/lgtm
/assign @olemarkus

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: olemarkus

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[olemarkus]

/retest

[k8s-ci-robot]

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

Test name	Commit	Details	Required	Rerun command
pull-kops-e2e-k8s-gce-cilium	e969b84	link	unknown	/test pull-kops-e2e-k8s-gce-cilium
pull-kops-e2e-k8s-aws-calico	e969b84	link	unknown	/test pull-kops-e2e-k8s-aws-calico

Full PR test history. Your PR dashboard. Please help us cut down on flakes by linking to an open issue when you hit one in your PR.

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[johngmyers]

/retest