[PowerShell] Deploy-FinOpsHub resets unspecified options on redeploy #2399

📝 Scenario

As a FinOps hub admin, I need Deploy-FinOpsHub to keep my existing hub's options on redeploy in order to upgrade without silently resetting settings I didn't re-specify.

⚠️ Problem

Deploy-FinOpsHub only passes the four retention values when you specify them (#2206, #2348). Every other option is always sent, so an unspecified option resets to the command's default on an existing hub: StorageSku (Premium_LRS), EnableManagedExports, EnableInfrastructureEncryption, EnablePurgeProtection (switches become false), VirtualNetworkAddressPrefix, ScopesToMonitor (empty), network mode (public), and tags. Recommendation options (enableRecommendations, enableAHBRecommendations, enableSpotRecommendations) can't be set from the command at all.

💎 Solution

Only send an option when the user specifies it, as retention already does, so the template keeps the current value; add the missing recommendation parameters. Where the template can't "keep current", read the existing hub and fill in the value.

📋 Tasks

• Pass options only when bound, for each option above
• Add recommendation parameters to Deploy-FinOpsHub
• Unit tests: redeploy without options does not change existing values
• Docs and changelog

✅ Acceptance

• Redeploying an existing hub with only -Name, -ResourceGroupName, and -Location leaves every option unchanged.

ℹ️ Additional context

Complements the parameter-file command in the portal upgrade issue. Raised in PR #2394 review.

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