[Feature request] Allow multiple instances/windows

[ThreeDeeJay]

The feature request

Would be nice to allow multiple independent instances/windows of GitHub for different projects so we can manage multiple repos at once. Especially useful when using multiple monitors/desktops.

Proposed solution

This was requested for the master branch nearly a decade ago in desktop#3606 but only recently implemented by someone in their own fork here:
Description by author + demo: desktop#3606 (comment)
Commit: desktop/desktop@development...hewigovens:github-desktop:repo-list-open-in-new-window

Additional context

No response

[pol-rivero]

I will need to investigate this thoroughly, to see if it's compatible with the way the auth callback is handled.
If everything works as expected, I see no problem cherry-picking this.