Update install docs for .NET 9

[adegeo]

Summary

Some stuff is unchanged as I'll need to capture screenshots and hashes for download files after they're released.

Fixes #43342
Fixes #43341
Fixes #42479

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📄 File	🔗 Preview link
docs/core/install/how-to-detect-installed-versions.md	How to check that .NET is already installed
docs/core/install/linux-alpine.md	Install .NET on Alpine
docs/core/install/linux-debian.md	Install the .NET SDK or the .NET Runtime on Debian
docs/core/install/linux-fedora.md	docs/core/install/linux-fedora
docs/core/install/linux-opensuse.md	Install the .NET SDK or the .NET Runtime on openSUSE Leap
docs/core/install/linux-rhel.md	Install .NET on RHEL and CentOS Stream
docs/core/install/linux-scripted-manual.md	Install .NET on Linux by using an install script or by extracting binaries
docs/core/install/linux-sles.md	docs/core/install/linux-sles
docs/core/install/linux-snap-runtime.md	Install .NET Runtime with Snap
docs/core/install/linux-snap-sdk.md	Install .NET SDK on Linux with Snap
docs/core/install/linux-ubuntu-install.md	Install .NET SDK or .NET Runtime on Ubuntu
docs/core/install/linux-ubuntu.md	Get OS version info which adds the $ID and $VERSION_ID variables
docs/core/install/localized-intellisense.md	docs/core/install/localized-intellisense
docs/core/install/macos-notarization-issues.md	macOS Catalina Notarization and the impact on .NET downloads and projects
docs/core/install/macos.md	Install .NET on macOS
docs/core/install/remove-runtime-sdk-versions.md	Remove the .NET runtime and SDK
docs/core/install/templates.md	Manage .NET project and item templates
docs/core/install/upgrade.md	docs/core/install/upgrade
docs/core/install/windows.md	Install .NET on Windows

[omajid]

Thank you for updating the RHEL install instructions too!

[adegeo]

No problem @omajid I try to keep it all up to date regardless. So if something is wrong, please let me know and I'll get working on it.

[omajid]

Everything is good, as far as I can tell! Thanks again!