core: motd - dynamically read OS version on each login

[MickLesk]

✍️ Description

Previously, OS name and version were captured at installation time and written statically to the MOTD profile script. After OS upgrades, the displayed version would still show the old version.

Now OS info is read dynamically from /etc/os-release on each login, similar to how hostname and IP are already handled.

Affects both Debian/Ubuntu (install.func) and Alpine (alpine-install.func).

🔗 Related Issue

Fixes #9711

✅ Prerequisites (X in brackets)

• Self-review completed – Code follows project standards.
• Tested thoroughly – Changes work as expected.
• No security risks – No hardcoded secrets, unnecessary privilege escalations, or permission issues.

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🛠️ Type of Change (X in brackets)

• 🐞 Bug fix – Resolves an issue without breaking functionality.
• ✨ New feature – Adds new, non-breaking functionality.
• 💥 Breaking change – Alters existing functionality in a way that may require updates.
• 🆕 New script – A fully functional and tested script or script set.
• 🌍 Website update – Changes to website-related JSON files or metadata.
• 🔧 Refactoring / Code Cleanup – Improves readability or maintainability without changing functionality.
• 📝 Documentation update – Changes to README, AppName.md, CONTRIBUTING.md, or other docs.

[CrazyWolf13]

nice!

I just tried for ages to write a single sed command to inject the new dynamic motd, but it seems impossible with all that string quotation.

I'll just update my docs