fix: point OpenShift documentation links at docs.redhat.com

[arska]

docs.openshift.com is a legacy domain with a four-hop redirect chain

Every link to it now goes through four redirects, two of which downgrade to plain HTTP, before reaching Red Hat's current documentation site:

https://docs.openshift.com/container-platform/
  -> http://docs.openshift.com/container-platform/latest      (301, downgrade)
  -> http://docs.openshift.com/container-platform/4.18/        (301)
  -> https://docs.openshift.com/container-platform/4.18/       (301, back up)
  -> http://docs.openshift.com/.../welcome/index.html          (301, down again)
  -> https://docs.redhat.com/en/documentation/openshift_container_platform/...

Linking the destination removes the chain, the protocol downgrades, and a version pin nobody chose: the bare /container-platform/ URL resolves to whatever Red Hat currently points it at, which is 4.18 today and will silently change.

13 occurrences across 9 files. The pages still render the same; only the hrefs change.

Where the replacements come from

Each one is where Red Hat's own redirect resolves that exact URL today, so the mapping is theirs rather than mine. Three needed a judgment call instead, and each was checked in a browser rather than guessed:

case	why	resolution
bare /container-platform/	redirect lands on 4.18/html/about/welcome-index, but that book 404s at latest (checked on 4.22)	product landing page, .../openshift_container_platform/latest
4.11 ServiceMonitor API	that version of the page is gone; the redirect gives up at the 4.11 version root	same page under latest, verified live
links that said latest	docs.redhat.com honours the same alias	still say latest, so nothing is newly pinned

I originally tried to verify all 13 targets with a script, using "does it redirect?" as the signal for a valid page. That check was worthless: docs.redhat.com answers 403 to every non-browser client regardless of user agent, and my known-dead control passed it exactly like the known-good one. The browser checks above are what the three judgment calls actually rest on.

Deliberately not changed

• Version-pinned links keep their version (3.11, 4.8, 4.9, 4.11), except the one whose page no longer exists there. Whether those are still the right versions to document against is an editorial question for maintainers, not a link fix.
• One anchor is dropped. accessing-the-registry.html#prerequisites has no corresponding fragment on the new page, so it lands at the top of the right chapter.

How it was found

The external link audit in vshn/landingpager#707 flagged the two occurrences on index.adoc as 403s. They are not dead links: docs.redhat.com blocks non-browser clients below the user-agent level, and the pages load fine in a browser. Excluding the domain from the link checker would have been the easy answer and would have left the redirect chain, the HTTP downgrades and the drifting version pin in place. The other 11 occurrences are the same problem on pages that audit does not reach.