Fixed the previous fix of the anti-nag hook and propagated fixes everywhere

[imcrazytwkr]

✍️ Description

The old fix of the anti-nag apt hook had some unintended side effects as reported today by @memesalot and @vsc55 in #6078. This PR fixes this. What is being done in particular:

• && chaining is replaced back with an if-condition because otherwise the hook returns with a non-0 exit code when JS patching is not needed and apt scares users with an error message
• dpkg -V check has been replaced with a grep -F check to avoid stdout leaking ??5?????? /usr/share/javascript/proxmox-widget-toolkit/proxmoxlib.js (I couldn't reproduce that on my installs, glad others helped with testing)
• Reverted the sed change that replaced ! with = back to just deleting ! to return compatibility with 8.0 (tested on 8.0.0 and 8.0.3) Thanks to @vsc55 for reporting!
• Propagated changes from pve-post-installer: remove Nag-File if already exist #6098 to the other proxmox post-install scripts (fixes Proxmox Backup Server Post Install no-nag-script on 3.4.3 does not disable subscription nag #6158)

🔗 Related PR / Issue

Link: #6078
Link: #6084
Link: #6095
Link: #6098
Link: #6158

✅ Prerequisites (X in brackets)

• Self-review completed – Code follows project standards.
• Tested thoroughly – Changes work as expected. Tested myself on 8.0.0, 8.0.3, 8.4.1 and 8.4.5. This time also tested by @vsc55 (message link) and @memesalot (message link)
• 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.

[imcrazytwkr]

Hi @vsc55! Can I bother you to test this one on 8.0 too just in case? I've tested it myself but the more eyes on the code, the better.

[vsc55]

Hi @vsc55! Can I bother you to test this one on 8.0 too just in case? I've tested it myself but the more eyes on the code, the better.

Hi @imcrazytwkr, I've tried it and it works perfectly. 👌