Add Oracle Linux installation instructions

[villepeh]

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I forgot the guide applies to Oracle Linux as well. In fact, I ran a small homeserver on OEL a few months back.

I did minimal installations on Rocky and OEL on VirtualBox and noticed Codeready/Powertools repos aren't required, so I removed those commands from the guide. I switched RHEL-references to EL.

#17423 was merged before I remembered about OEL but a new PR shouldn't hurt :)

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