Rename supported operating systems and add note for Alma

What does this MR do and why?

This MR is to reformat the operating system docs page so the supported operating systems are listed on the top and the page is titled "supported OS".

Also adding a note for support of Alma as a replacement for CentOS as it nears EOL

Describe in detail what your merge request does and why.

Screenshots or screen recordings

These are strongly recommended to assist reviewers and reduce the time to merge your change.

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.