New script: Local Certificate Authority based upon Smallstep's step-ca

[reelsense]

✍️ Description

Thanks to @fwiegerinck: This pull request refactors and fixes the previously closed PR #1655 for the Smallstep step-ca script. The original submission was not merged due to non-compliance with the project's contribution standards.

This new version addresses all feedback from the original PR thread:

• Correct Script Structure: The interactive whiptail setup dialogs have been moved from ct/alpine-step-ca.sh into install/alpine-step-ca-install.sh, as requested. The ct script now correctly serves only to define container variables and initiate the build.
• Safe Update Handling: The previous, unsafe update_script has been replaced with the standard "no-update" function. This aligns with updateable: false in the JSON file and prevents users from accidentally breaking their CA with a simple package upgrade.
• Code Standardization: The installation script has been overhauled to use the project's standard functions (msg_info, msg_ok) and variables ($STD) for consistent output and behavior.
• Improved User Experience: The final MOTD message now correctly displays the CA fingerprint and ACME URL (if enabled) to guide the user on how to start using their new CA.

These changes bring the script set into full compliance with the contribution guidelines, making it safe, maintainable, and ready for merging.

🔗 Related PR / Issue

Fixes and supersedes #1655

✅ 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.

[MickLesk]

There is an First-Line Message: "🛑 New scripts must be submitted to ProxmoxVED for testing.
PRs without prior testing will be closed."

=> So create there an PR, not in the LiveRepo
Or increase this one: community-scripts/ProxmoxVED#799