[rotang] Add an option to create FullDay shifts in Google Calendar.

Turns out a bunch of rotatins use, and like, to have the events scheduled
as FullDay events in the Google Calendar.

- Add an option for FullDay events in the rotation configuration.
- UI to enable/disable the option.
- Code to create calendar DateTime events adhering to the new option.
- Snuck in a change so the staging env. does not send Notification invites
  on event creation.

Bug: 918960
Change-Id: I238649df72f444cd82422aa7512076ad0086b7ea
Reviewed-on: https://chromium-review.googlesource.com/c/1455557
Reviewed-by: Scott Lewis-Kelly <slewiskelly@google.com>
Commit-Queue: Ola Karlsson <olakar@chromium.org>
Cr-Commit-Position: refs/heads/master@{#20537}