Add switch to `force:org:open` to open the org in an incognito window

[jclark-dot-org]

Is your feature request related to a problem? Please describe.
When testing certain scenarios, it is often advantageous to use an incognito browser session to eliminate any overlap with existing sessions.

What are you trying to do
Open a linked org in an incognito browser window.

Describe the solution you'd like
The org is opened in an incognito browser window.

Describe alternatives you've considered
As a workaround, I currently run force:source:open -r and paste the resultant URL into a new browser window. This would just be a nice-to-have.

Additional context
N/A

[ntotten]

While I like this idea, there isn't any way to do this cross-browser. Each browser has a different flag or method of doing this so we would have to know which browser is being opened, which we dont.