[ Workers/ Workflows ] Add Workflows test support APIs

[pombosilva]

Summary

Added two new APIs for Workflow testing in the /workers/testing/vitest-integration/test-apis directory. A link to these APIs has also been added to the Workflows page.

Screenshots (optional)

Test apis Workflows insertion:

Link in workflows page:

Documentation checklist

• 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 documentation style guide has been adhered to.
• If a larger change - such as adding a new page- an issue has been opened in relation to any incorrect or out of date information that this PR fixes.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.