Fix: Allow --config to specify a custom configuration path

[ErwannCodes]

Resolving the Issue: Using --config for a Custom Configuration Path
Problem: When a user specified the --config option with khal configure, the configuration file was always created in ~/.config/khal/config, even if a valid custom path was provided.

Identified Causes:

The value of --config was not correctly passed to configwizard.
Permissions for the specified path were not checked, leading to silent errors or failures.

Solution Provided
Correctly Passing --config:

The configure command now properly passes the --config value to configwizard.
configwizard uses this value to create or validate the configuration file.

Permission Handling:

If the specified path does not exist, it is automatically created.
If the necessary permissions are not available, a clear error message is displayed.

Handling Existing Files:

If a configuration file already exists at the specified path, a critical message is displayed, and the process is aborted to prevent overwriting.