Added checkout directory parameter to repo command

[TimVinkemeier]

✨ What kind of change does this PR introduce? (Bug fix, feature, docs update...)

A feature for setting the directory to check out to via a command line parameter in the repo command.

⤵️ What is the current behavior?

Currently, the repo command creates a temporary folder below %APPDATA% to check out the repository to.

🆕 What is the new behavior (if this is a feature change)?

The default is still the same. However, via the optional command line parameter --checkoutdirectory (or -cdir) a custom directory can be provided, e.g. nukeeper repo <url> <token> -cdir "C:\Git".

💥 Does this PR introduce a breaking change?

I don't think so, since the default behaviour is not changed and the command line switch is optional.

🐛 Recommendations for testing

📝 Links to relevant issues/docs

This solves the original request from #683 (though not the updated intention).
Although I tried setting the TMP-Variable as mentioned in the issue, the path with auto-generated temp folder names is still too long for óur project (I know, that is a discussion for itself), which is why I implemented this.

🤔 Checklist before submitting

• All projects build
• Relevant documentation was updated
  -> Please point me to the right documentation, I will be glad to update it 😃

This is my first PR here, so feel free to highlight any changes I should make (e.g. code style) and I will try to adjust them shortly...

[AnthonySteele]

Looks OK, can you rebase for the conflict?
Apologies for the delay, we are picking up again and clearing stale issues, but keeping this one.

[TimVinkemeier]

Done (hopefully I did it right).
No problem, still happy to have it accepted :)