Added Email of Keystone to Identity (#1681)

* Added Email of Keystone to Identity

After the successful login to keystone, the Email of the logged in user
is fetch from keystone and provided to `identity.Email`.

This is useful for upstream software that uses the Email as the primary
identification.

* Removed unnecessary code from getUsers

* Changed creation of userResponse in keystone

* Fixing linter error

Co-authored-by: Christoph Glaubitz <christoph.glaubitz@innovo-cloud.de>