OCPEDGE-1825: [TNF] Reworked TNF logic to render fencing block conditionally.

[jaypoulz]

Two Node OpenShift with Fencing (TNF) is a deployment topology with two control-plane nodes that was introduce as a Dev Preview in OpenShift 4.19. This commit updates the logic around TNF to only render fencing credentials in releases 4.19 and up, and also the sslInsecure parameter so that it uses certificateVerification in 4.20 and up, as introduced in openshift/installer#9640.

[openshift-ci]

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[openshift-ci]

Hi @jaypoulz. Thanks for your PR.

I'm waiting for a openshift-metal3 member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

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