refactor centos to opensuse migration (#485)

[Hooverdan96]

Continuation of PR #507
Fixes #485

This pull request's proposal

• rename file (commit bd05b9f78e635070bafe1dfd44644e9b41481c54)
• move to more generic CentOS to openSUSE description (commit ac1e2451dee64cb99acf8f41a0503b631ec44f00)
  • refactor text to remove v4 references, where applicable, and refer more to openSUSE versions.
  • semantic line break updates
  • replaced you/us/we with other terms/constructs.
• update toctree, file references and add entry to redirect.txt file (commit 012711fd1179ffd404bcdd27c2dc91e3327a57e7)

Checklist

• With the proposed changes no Sphinx errors or warnings are generated.
• I have added my name to the AUTHORS file, if required (descending alphabetical order).

[phillxnet]

@Hooverdan96 Thanks for the extra work re splitting out the re-name. This worked to enable me to view the content change in abstraction of the name change. Enabling a far easier review of that change. We should likely have this as a directive in our contributor docs as it makes for better git history and use of the GitHub Web-UI to do proper reviews.

I've only suggested one more change in this pass. Essentially you removed the read-only caveat we had in <= Leap 15.5 in text body, but we had a remaining reference to this in the follow-up warning re "This is an upstream dicision ..." so once that is removed as per my suggestion, if you agree, I can finally get this merged and published.

See what you think. And thanks again for the extra effort in asserting our apparent need re git mv when renaming files whos contents likely also changes. Plus the likely need then to also have this explicitly recorded via a non-squashed git commit.

Some nice improvements in language here, and it's good that we can now be looking back on this upgrade. NAS installs are sticky, so I like to have a long tail in our docs for folks only now getting around to our newer offering re "Built on openSUSE".

[Hooverdan96]

@phillxnet Thanks for proof-reading once more.

[phillxnet]

PR product PRODUCTION published.

Just a minor note here, we do contextually acknowledge our use of "openSUSE versions" are referencing our "Built on openSUSE" and the "OpenSUSE Installer" is followed directly with a reference to our "Rockstor's "Built on openSUSE". But we may want to re-visit this doc and make more 'marks aware' our use of the
"openSUSE" mark re the terms we acknowledge in our installer docs.

We should always take care to not claim we are openSUSE is my point. But we do that very clearly everywhere else. But I think this new doc version is cutting it a little close re the explicity title use of the "openSUSE" mark.

See: https://rockstor.com/eula.html (Our EULA) which in turn links to:

https://en.opensuse.org/openSUSE:Trademark_guidelines

I'll present a PR to amend our use, in sub-titles at least, of what I'd not realised in the review is a little too close for comfort re marks as outlined in the above.