chore: Enhance OpenAPI documentation by adding required field formatting and providing a description for the bearerAuth security scheme.

[skeptrunedev]

Documentation changes

Adds a link to where to get the API key into the API reference pages for the discovery endpoints of search and assistant.

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For Reviewers

When reviewing documentation PRs, please consider:

✅ Technical accuracy

• Code examples work as written
• Commands and configurations are correct
• Links resolve to the right destinations
• Prerequisites and requirements are accurate

✅ Clarity and completeness

• Instructions are clear and easy to follow
• Steps are in logical order
• Nothing important is missing
• Examples help illustrate the concepts

✅ User experience

• A new user could follow these docs successfully
• Common gotchas or edge cases are addressed
• Error messages or troubleshooting guidance is helpful