Add guide for ceph to be the object storage gateway for swift

[James]

This is a guide to add object storage via radosgw for swift.

This bug tracker is for errors with the documentation, use the following as a template and remove or add fields as you see fit. Convert [ ] into [x] to check boxes:

- [ ] This doc is inaccurate in this way: ______
- [x] This is a doc addition request.
- [ ] I have a fix to the document that I can paste below including example: input and output.

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Release: 13.0.2.dev106 on 2021-01-18 23:14:14
SHA: 6e982e076a19a70490fd047ada7c3cad2117ab39
Source: https://opendev.org/openstack/kolla-ansible/src/doc/source/reference/storage/swift-guide.rst
URL: https://docs.openstack.org/kolla-ansible/xena/reference/storage/swift-guide.html

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.opendev.org/c/openstack/kolla-ansible/+/839269

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.opendev.org/c/openstack/kolla-ansible/+/839273

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.opendev.org/c/openstack/kolla-ansible/+/839400

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.opendev.org/c/openstack/kolla-ansible/+/839418

[OpenStack Infra (hudson-openstack)]

Change abandoned by "James <email address hidden>" on branch: master
Review: https://review.opendev.org/c/openstack/kolla-ansible/+/839272
Reason: mistake

[OpenStack Infra (hudson-openstack)]

Change abandoned by "James <email address hidden>" on branch: master
Review: https://review.opendev.org/c/openstack/kolla-ansible/+/839273
Reason: Please refer to Change-Id: I71e23cab1ab78899a4a813c4eb56cea2c42170c8