Document manifest and storage backend operations

[gboutry]

No description provided.

[Copilot]

Pull request overview

Adds documentation for configuring and operating storage backends via the deployment manifest and Sunbeam operational procedures, expanding the ops guide to cover Pure Storage and gated (feature-flagged) in-tree backends.

Changes:

• Documented storage: manifest structure for DellSC, Hitachi, and Pure Storage backends.
• Added new operations guides for deploying a Pure Storage backend and enabling gated storage backends.
• Updated the Operations toctree to include the new guides.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 2 comments.

File	Description
reference/manifest-file-reference.rst	Adds a new storage: section describing backend config structure and example keys.
how-to/operations/index.rst	Registers new storage backend operation pages in the Operations toctree.
how-to/operations/enable-a-gated-storage-backend.rst	New how-to explaining feature-gate unlock and deployment workflow for gated backends.
how-to/operations/deploy-pure-storage-backend.rst	New how-to detailing Pure Storage backend deployment and configuration keys.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

You can also share your feedback on Copilot code review. Take the survey.

[Copilot]

The Pure Storage how-to mentions configuring pure-nvme-transport, but the manifest reference’s purestorage config key list omits it. Please align these docs (either document pure-nvme-transport in the manifest reference, or remove/adjust the how-to guidance if it isn’t a supported key).

Suggested change

	For NVMe/TCP deployments, you can also set ``pure-nvme-cidr`` and
	``pure-nvme-transport``. Only ``tcp`` is supported for
	``pure-nvme-transport``.
	For NVMe/TCP deployments, you can also set ``pure-nvme-cidr`` to specify the
	NVMe/TCP network used by the array. NVMe transport is TCP.