[Docs] Illustrate cloud/security/keychains with Zara's Infrastructure team keychain

[leecalcote]

Overview

Update cloud/security/keychains to use Zara Osei configuring a keychain scoped to the Orbital Labs Infrastructure team, controlling access to the prod-aws environment.

Tasks

• Add scenario: Zara creates a keychain for the Infrastructure team
• Show keychain scoped to orbital-production workspace and prod-aws environment
• Add screenshot (log in as Zara: zara@orbital-labs.example) per screenshot standards at /cloud/about/five-narrative-plan
• Link to /cloud/about for cast context

Reference

• Narrative: /cloud/about
• Difficulty: Medium