Improve dnf installation instructions to clarify which version to use #9975

We have received some issues and PRs regarding the dnf installation instructions not working. The cause is users not following the installation instructions corresponding to the version of dnf they have installed:

• Commands not working for installing gh-cli on Red Hat Enterprise Linux 9.5 (Plow) #9974
• Command issue for Fedora and centos #9965
• Correct command to add gh-cli repo to dnf config #9943

We should improve the installation instructions to encourage users to understand which dnf version they have installed and clearly describe which installation commands to use for that version.

Some improvement thoughts:

• The note about which version of dnf to use comes after the commands to run (people do not read that far since they just want a command to copy/paste)
• The dnf4 instructions are collapsed. Perhaps they should be un-collapsed for now since most people will still be using dn4 until the majority upgrade to OS versions with dnf5 by default.
• Both instructions should be under subheadings that clearly indicate the dnf versions

Expected output

The the dnf installation instructions are improved to prevent users from running the wrong installation command for their dnf version.