Add Nushell support

[doubleailes]

Is your feature request related to a problem? Please describe.
Using a unify ( win/linux) modern shell with Spk

Describe the solution you'd like
An implementation of Nushell in Spk

Describe alternatives you've considered
Use powershell also with linux but it not that interesting

Additional context
...

[doubleailes]

Following the Slack discussion the todo to implement Nushell in Spk should be:

• spfs startup script to initialize the shell inside a new runtime
• spfs activation scripts generated by spk

It generate two issues with Nushell

• Restriction autoload to only nu files
  • Released in version 0.97.1
• Autoload directories using --commands
  • Released in version ?

Here is a draft PR: #1106 to start discussion in parallel of Nushell's team to add the fix/features

[doubleailes]

The PR nushell/nushell#15679 add to Nushell the required feature.