feat(docs): private API Gateway tutorial to Guides

[revitalbarletz]

Checklist

• Title matches Winglang's style guide
• Description explains motivation and solution
• Tests added (always)
• Docs updated (only required for features)
• Added pr/e2e-full label if this feature requires end-to-end testing

By submitting this pull request, I confirm that my contribution is made under the terms of the Wing Cloud Contribution License.

[github-actions]

Thanks for opening this pull request! 🎉
Please consult the contributing guidelines for details on how to contribute to this project.
If you need any assistence, don't hesitate to ping the relevant owner over Slack.

Topic	Owner
Wing SDK and utility APIs	@chriscbr
Wing Console	@ainvoner, @skyrpex, @polamoros
JSON, structs, primitives and collections	@hasanaburayyan
Platforms and plugins	@hasanaburayyan
Frontend resources (website, react, etc)	@tsuf239
Language design	@eladb
VSCode extension and language server	@markmcculloh
Compiler architecture, inflights, lifting	@yoav-steinberg
Wing Testing Framework	@tsuf239
Wing CLI	@markmcculloh
Build system, dev environment, releases	@markmcculloh
Library Ecosystem	@chriscbr
Documentation	@hasanaburayyan
SDK test suite	@tsuf239
Examples	@hasanaburayyan
Wing Playground	@eladcon

[mergify]

Thanks for contributing, @revitalbarletz! This PR will now be added to the merge queue, or immediately merged if revitalbarletz-patch-1 is up-to-date with main and the queue is empty.

[monadabot]

Congrats! 🚀 This was released in Wing 0.61.21.