Add an option in DevDiagnostics Settings where the user can change the hotkey to her preferred key combination

[andreww-msft]

Suggested new feature or improvement

PI ships with a pre-defined hotkey combination (Windows-F12). This was chosen for several reasons:

1. Key combinations with the Windows key are the least likely to conflict with any app-defined keys.
2. F12 echoes the Edge F12 key for developer diagnostics.
3. Limiting the key combination to 2 keys makes it easier and faster to use.
4. While F* keys are problematic on some laptop keyboards (involving an additional function key), most developers will likely have full-size machines with full-size keyboards.

That said, one of our guiding principles is to enable user-configuration. So allowing the user to choose her own preferred key combinations is entirely reasonable.

Also see related #3466