Update AOE documentation to show automation variable name for multiple workspaces

[mpritchard2]

🛠️ Description

MS Learn documentation for using multiple workspaces for performance logs references a new automation variable, but it does not list it. Screenshot included in doc has the variable cut off. This PR updates documentation to include the variable name.

📋 Checklist

🔬 How did you test this change?

• 🤏 Lint tests
• 🤞 PS -WhatIf / az validate
• 👍 Manually deployed + verified
• 💪 Unit tests
• 🙌 Integration tests

🙋‍♀️ Do any of the following that apply?

• 🚨 This is a breaking change.
• 🤏 The change is less than 20 lines of code.

📑 Did you update docs/changelog.md?

• ✅ Updated changelog (required for dev PRs)
• ➡️ Will add log in a future PR (feature branch PRs only)
• ❎ Log not needed (small/internal change)

📖 Did you update documentation?

• ✅ Public docs in docs (required for dev)
• ✅ Internal dev docs in src (required for dev)
• ➡️ Will add docs in a future PR (feature branch PRs only)
• ❎ Docs not needed (small/internal change)

[MSBrett]

LGTM - Variable name verified in codebase at src/optimization-engine/runbooks/recommendations/Recommend-AdvisorCostAugmentedToBlobStorage.ps1:184. Documentation improvement resolves the missing variable name issue.

[microsoft-github-policy-service]

@all-contributors please add @mpritchard2 for doc

[allcontributors]

@microsoft-github-policy-service[bot]

I've put up a pull request to add @mpritchard2! 🎉