[Optimization engine] Improve Storage Account access and interactive scripts security

[helderpinto]

🛠️ Description

Align AOE with security best practices, by:

1. Avoiding the usage of Storage Account keys to access blob data by Automation runbooks. The Automation managed identity is now granted the Storage Blob Data Contributor role and all runbooks authenticate using Microsoft Entra ID credentials.
2. Using the AsSecureString parameter in the Get-AzAccessToken calls in the interactive scripts (over which we have less PS modules version control).

Fixes #975

📋 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)