How to deploy Ceph into existing overcloud in Red Hat OpenStack Platform?

Issue

• How to deploy a new Ceph storage environment alongside an already deployed overcloud?
• How to integrate Ceph storage environment into an existing overcloud?
• There's documentation on how to deploy an overcloud with ceph, and how to deploy an overcloud while integrating an existing ceph storage environment, but nothing on deploying ceph after an overcloud environment has already been created.