Create a group gerrit-flows with runAs+viewAllAccounts permission

Following go/gob/users/gerrit-flows#onboarding step 5/6, except that
says to grant the *user* permission but the Gerrit UI doesn't allow me
to do that, so I created a group and added the user instead.
Group:
https://dawn-review.git.corp.google.com/admin/groups/e6a605e72c494a2fbf0c51f14cd0f24fb7ae1e50,members
User: https://dawn-review.git.corp.google.com/dashboard/4718297

Bug: 493938721
Change-Id: I7da16e9bc47043d78f2f6ffcaef80df544d4205b