Add a global capability to allow generating HTTP passwords

The capability `generateHttpPassword` allows non-administrator
users to generate HTTP passwords for users other than self.

This capability would typically be assigned to a non-interactive
group to be able to register HTTP passwords for users from a
tool or web service that uses the Gerrit REST API.

Change-Id: I3d77cd406b0258d68cd0b8bb4dfbdcec97112450
4 files changed