Add docs for steps that return readable streams

[Caio-Nogueira]

Summary

We're adding the option of returning a ReadableStream<Uint8Array> from workflow steps. This PR adds documentation, with examples and usage guidelines for this new pattern

• Is there a changelog entry (guidelines)? If you don't add one for something awesome and new (however small) — how will our customers find out? Changelogs are automatically posted to RSS feeds, the Discord, and X.
• The change adheres to the documentation style guide.
• If a larger change - such as adding a new page- an issue has been opened in relation to any incorrect or out of date information that this PR fixes.
• Files which have changed name or location have been allocated redirects.

[github-actions]

This pull request requires reviews from CODEOWNERS as it changes files that match the following patterns:

Pattern	Owners
/src/content/docs/workflows/	@elithrar, @celso, @mia303, @jonesphillip, @cloudflare/pcx-technical-writing
*	@cloudflare/pcx-technical-writing

[github-actions]

Preview URL: https://f41822a9.preview.developers.cloudflare.com
Preview Branch URL: https://caio-workflows-readable-stream.preview.developers.cloudflare.com

Files with changes (up to 15)

Original Link	Updated Link
https://developers.cloudflare.com/workflows/reference/limits/	https://caio-workflows-readable-stream.preview.developers.cloudflare.com/workflows/reference/limits/
https://developers.cloudflare.com/workflows/build/workers-api/	https://caio-workflows-readable-stream.preview.developers.cloudflare.com/workflows/build/workers-api/
https://developers.cloudflare.com/workflows/get-started/guide/	https://caio-workflows-readable-stream.preview.developers.cloudflare.com/workflows/get-started/guide/
https://developers.cloudflare.com/workflows/build/rules-of-workflows/	https://caio-workflows-readable-stream.preview.developers.cloudflare.com/workflows/build/rules-of-workflows/