Prebuilts API is missing from the OpenAPI doc

[czechboy0]

Describe the bug

The new experimental prebuilts API is missing from the OpenAPI doc: https://github.com/swiftlang/swift-org-website/blob/main/openapi/downloadswiftorg.yaml

To Reproduce

Open https://www.swift.org/openapi/openapi.html?urls.primaryName=download.swift.org+API

Expected behavior

The prebuilts APIs would be documented there.

Actual behavior

Not documented.

[czechboy0]

cc @dschaefer2