Add DPS stable 2026-08-31 API (#44708)

* Add DPS stable 2026-08-01 API

Port Microsoft.Devices/DeviceProvisioningServices stable 2026-08-01 API changes from the private specs-pr branch.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Copilot-Session: 8c2992b1-f953-42ea-b0e5-94828091765c

* Remove DPS device registry namespace from 2026-08-01

Remove deviceRegistryNamespace from the stable 2026-08-01 API version while preserving it in earlier preview versions.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Copilot-Session: 8c2992b1-f953-42ea-b0e5-94828091765c

* Rename DPS stable API version 2026-08-01 to 2026-08-31

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Copilot-Session: 4617d7b5-4b5e-4704-93a5-755bd47d4738

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Co-authored-by: Molly Iverson <mollyiverson@microsoft.com>
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Copilot-Session: 8c2992b1-f953-42ea-b0e5-94828091765c
Copilot-Session: 4617d7b5-4b5e-4704-93a5-755bd47d4738