[PowerShell] Deploy-FinOpsHub should use the self-contained template for latest #2398

📝 Scenario

As a FinOps hub admin, I need Deploy-FinOpsHub to use the latest self-contained template by default in order to deploy without downloading and compiling a release package.

⚠️ Problem

Deploy-FinOpsHub -Version latest (the default) calls the GitHub releases API, takes the first stable release, downloads the finops-hub-v<version>.zip package, and deploys its main.bicep with New-AzResourceGroupDeployment. That adds a dependency on the GitHub API (rate limits, proxies) and the Bicep CLI, and the same releases lookup is used for named versions.

💎 Solution

• latest (no -Version): deploy the self-contained compiled template (a single JSON file; latest is always self-contained). No release lookup.
• Named, non-latest versions (for example -Version 14.0): keep using GitHub releases.
• -Preview keeps working for named preview versions.

📋 Tasks

• Update Deploy-FinOpsHub (and Save-FinOpsHubTemplate if needed) so latest skips the releases lookup
• Confirm the self-contained template location is stable and always current
• Unit tests for latest and named versions; update the docs-mslearn page and changelog

✅ Acceptance

• Deploy-FinOpsHub with no -Version makes no GitHub releases API call.
• -Version <named> still deploys that release.

ℹ️ Additional context

Related: #257 (local template), #2215 (JSON deployment size error). Raised in PR #2394 review.

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