[Hubs] Document remote hubs support and add UI configuration

[Copilot]

This PR implements comprehensive documentation and UI support for remote hubs (cross-tenant) functionality in FinOps hubs.

Problem

Remote hubs support was added to the backend infrastructure but was never fully documented or accessible through the UI deployment form. Users had no guidance on how to configure cross-tenant scenarios where satellite hubs send data to a central primary hub.

Solution

1. UI Form Enhancement

• Added Remote hub configuration section to the Advanced step in createUiDefinition.json
• Added remoteHubStorageUri field with Data Lake storage URI validation
• Added remoteHubStorageKey field as secure password input with storage key validation
• Properly configured outputs to pass parameters to the deployment template

2. Comprehensive Documentation

• Added new section "Optional: Configure remote hubs" to the main deployment guide
• Documented when to use remote hubs (multi-tenant scenarios)
• Explained architecture with primary and satellite hub concepts
• Provided step-by-step configuration for both Azure portal and PowerShell
• Included security considerations and best practices

3. PowerShell Documentation Updates

• Updated Deploy-FinOpsHub command syntax to include remote hub parameters
• Enhanced parameters table with detailed descriptions and examples
• Added complete deployment example for remote hub scenarios

4. Enhanced Template Documentation

• Improved parameter descriptions for remoteHubStorageUri and remoteHubStorageKey
• Added clear instructions for obtaining values from the primary hub
• Documented version requirements (0.4+) and security implications

Key Features

• Cross-tenant support: Enable cost data aggregation across multiple Azure tenants
• Secure configuration: Proper handling of storage keys as secure parameters
• Complete guidance: End-to-end instructions for both portal and PowerShell deployment
• Architecture clarity: Clear explanation of primary vs satellite hub roles

Configuration Parameters

• remoteHubStorageUri: Data Lake storage endpoint from primary hub (e.g., https://primaryhub.dfs.core.windows.net/)
• remoteHubStorageKey: Storage account access key from primary hub

Usage Example

Deploy-FinOpsHub `
    -Name MyRemoteHub `
    -ResourceGroup MyRemoteHubResourceGroup `
    -Location westus `
    -RemoteHubStorageUri "https://centralhub.dfs.core.windows.net/" `
    -RemoteHubStorageKey "storage-key-here"

The backend implementation already existed - this PR completes the user-facing documentation and UI integration to make remote hubs fully accessible and properly documented.

Fixes #1093.

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[flanakin]

Move this into a separate configure-remote-hubs.md file. Keep a placeholder "Plan for multiple tenants and clouds" section here that links out to the full document. Make sure it calls out that remote hubs can be used for multiple tenants in the same Azure cloud or tenants in different Azure clouds. Supported clouds are:

• Azure Commercial
• Azure Government
• Azure China

[Copilot]

Moved the remote hubs content to a separate configure-remote-hubs.md file and replaced with a "Plan for multiple tenants and clouds" section that links to the detailed guide. Added explicit support for Azure Commercial, Azure Government, and Azure China as requested. (97867b7)

[flanakin]

Move the "Copy from..." instructions to the Configure remote hubs page. That doesn't need to be here.

[Copilot]

Removed the "Copy from..." instructions from the template.md parameter descriptions. These instructions are now in the Configure remote hubs page. (97867b7)

[flanakin]

Move this down to the deploy the template section as a subbullet under the Azure portal template deployment.

[Copilot]

Moved the Azure portal remote hub configuration instructions to the deploy template section as a subbullet under step 14 of the Azure portal deployment. (97867b7)

[flanakin]

Make sure these changes are applied to the Deploy-FinOpsHub.ps1 PowerShell command and that there's also a unit test to verify the parameters are set correctly.

[Copilot]

Verified that the Deploy-FinOpsHub.ps1 PowerShell command already includes the remote hub parameters correctly and added comprehensive unit tests to verify the parameters are set correctly for individual and combined remote hub scenarios. (97867b7)