Add interactive uitest for incognito menu items

This CL is migrating P0 manual test "Check Launching an incognito window"[1] to interactive_uitest using Kombucha.

The original testcase description:

Procedure:
1. Go to chrome menu --> Select New Incognito window
2. Try launching an incognito window via CTRL+SHIFT+N / Command+Shift+N

Verification:
An incognito window should be launched successfully in both the steps above.
Chrome should not crash upon navigating to an Incognito Window.

[1]
https://testtracker.googleplex.com/testplans/testcase/detail/3459147?id=27299&revision=46

Change-Id: I114f889a36b56bc60386c8ea6f933700c93f7f31
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4054980
Reviewed-by: Dana Fried <dfried@chromium.org>
Commit-Queue: Kuan Huang <kuanhuang@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1079431}