Explicitly label CRW for Z and P as Tech Preview in release notes and install guides

In the RN and in the IG, we only mention the Technical Preview support level of CRW for Z, and only in the context of airgap support.

We should call this out more explicitly in more places so it's not a buried footnote.

From David H:

If we’re going to update the docs personally I’d say:
“Support for deploying CodeReady Workspaces on OpenShift Container Platform on [IBM Z/IBM Power] is currently only available as a Technical Preview release.”
should become a statement immediately following the 4.1/4.2 sections here rather than buried in the airgap limitation.

Would also need to slightly reword the airgap section as a result.

I’m also surprised we havent called out Z/P as tech preview here

https://access.redhat.com/documentation/en-us/red_hat_codeready_workspaces/2.7/html/installation_guide/supported-platforms_crw