SuperSlicer should pass the datadir parameter when launching new instance

[Drachenkaetzchen]

Describe the bug
When I use the Window > Open New Instance function, SuperSlicer does not pass the datadir parameter to the new instance.

To Reproduce
Steps to reproduce the behavior:

1. Launch SuperSlicer using a datadir parameter, for example: superslicer.exe --datadir settings
2. Use Window > Open New Instance
3. In the newly opened instance, use Help > Show Configuration Directory
4. The default configuration directory will be shown, instead of the datadir passed above

>> Project File <<
Not applicable.

Expected behavior

If SuperSlicer is launched using a datadir parameter, that parameter should be passed to other instances as well.

Screenshots
Not applicable.

Desktop (please complete the following information):

• OS: Windows 10
• Version 2.3.56.7