[API] Update create-lxc.sh / Improve error messages #1

[michelroegl-brunner]

✍️ Description

This PR updates create-lxc.sh and reworks the error messages.
Befor it was just error "some string", but this never kills the the spinner and leaves the shell in a unwanted state.

I´ve updated the error messages to use msg_error "some string" to better handel this case.

In preperation for better error messages each error gets its own designated error code, to send the correct message to the api.

✅ Prerequisites

The following steps must be completed for the pull request to be considered:

• Self-review performed (I have reviewed my code to ensure it follows established patterns and conventions.)
• Testing performed (I have thoroughly tested my changes and verified expected functionality.)

🛠️ Type of Change

Please check the relevant options:

• [] Bug fix (non-breaking change that resolves an issue)
• New feature (non-breaking change that adds functionality)
• [] Breaking change (fix or feature that would cause existing functionality to change unexpectedly)
• [] New script (a fully functional and thoroughly tested script or set of scripts)

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📋 Additional Information (optional)

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After change: