Update status on Linux docs

[adegeo]

• Removed the "not yet available" note where the packages are now available.
• Converted some of the sections that had install .net 8/9 to tabs.
• Updated information about the backports repository.
• Removed distros that are no longer supported or about to go out of support.

---

Internal previews

Toggle expand/collapse

📄 File	🔗 Preview link
docs/core/install/linux-alpine.md	Install the .NET SDK or the .NET Runtime on Alpine
docs/core/install/linux-debian.md	[.NET 9](https://review.learn.microsoft.com/en-us/dotnet/core/install/linux-debian?branch=pr-en-us-43671)
docs/core/install/linux-fedora.md	Install .NET on Fedora
docs/core/install/linux-opensuse.md	Install the .NET SDK or the .NET Runtime on openSUSE Leap
docs/core/install/linux-rhel.md	docs/core/install/linux-rhel
docs/core/install/linux-sles.md	Install the .NET SDK or the .NET Runtime on 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/macos.md	Install .NET on macOS
docs/core/install/windows.md	docs/core/install/windows