Allow merge commits for operations-guide

In order to support third-party editing on a feature/edits branch of
openstack/operations-guide, the openstack-doc-ptl group is granted
access to push merge commits. This will facilitate periodic
synchronization of state between feature/edits and master branches
until such time as the feature branch is no longer needed.

Change-Id: I028c61dbd1eb6112097b111eb9645b81c24e32e0
Merge "Allow merge commits for operations-guide"