fix: whitelist var_searchdomain and fix the handling of var_ns and va…

[tommoyer]

✍️ Description

Currently misc/build.func does not allow setting var_searchdomain because it is not in the whitelist. Then var_ns and var_searchdomain are not properly set with the right flags when creating PCT_OPTIONS_STRING

✅ 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.

[michelroegl-brunner]

@MickLesk also check please.

[MickLesk]

should be okay, i dont use it. so the user should report afterwards