Remove refs to master in RT kernel

[bobfuru]

Per Go/No Go meeting on 14 Oct:

1887007 Creating cluster with realtime kernel almost always fails. Moved to RHEL 8. Not a blocker for 4.6 per Mark M.
Requires documentation update:

• (Xiaoli) For this one, we need to make sure we have explicit documentation to indicate that RT kernel is only supported on worker nodes so far.
• (Tim R) Simply put, "No support for RT on control plane nodes", that statement would then include 3 node configurations etc. +1 Jeff L
• (Jeff L) RT kernel team says they were told only worker nodes. The docs say worker or master, but should only say worker for RAN use cases only.

Hence, this PR removes reference to master and control plane in body text and example output.

I also reorganized text in the overview so that items are in a bulleted list, with a note about worker-only/RAN-only support for RT kernel.

@jtligon and @marrusl PTAL and let me know if this looks good to you. Thanks!

[openshift-docs-preview-bot]

The preview will be available shortly at:

• https://rt-kernel-updates--ocpdocs.netlify.com/

[kalexand-rh]

Two small things, then it LGTM!

[bobfuru]

Approved by PM and Dev via Slack.

[bobfuru]

/cherrypick enterprise-4.6

[openshift-cherrypick-robot]

@bobfuru: new pull request created: #26513

Details

In response to this:

/cherrypick enterprise-4.6

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/test-infra repository.