fix: Optimize the network module for Researcher

[Prekshith-Microsoft]

This pull request refactors the Azure infrastructure Bicep modules to improve clarity, modularity, and maintainability of private networking resources. The main changes include replacing the monolithic network.bicep module with a more focused virtualNetwork.bicep module, updating parameter names for consistency, and ensuring all resource references use the new module outputs. Additionally, Azure Bastion Host and Jumpbox VM provisioning logic is now handled directly in main.bicep, and all dependent resources have been updated to reference the new output names and structures.

Network module refactoring and resource provisioning:

• Removed the legacy network.bicep module and its outputs, replacing it with a new virtualNetwork.bicep module that provides more granular outputs for each subnet and resource, improving modularity and clarity. (infra/modules/network.bicep)
• Updated the main deployment logic to use the new virtualNetwork module, and added direct provisioning for Azure Bastion Host and Jumpbox VM resources in main.bicep, with improved parameter naming and resource referencing.

Parameter and variable renaming for consistency:

• Renamed VM admin username and password parameters from vmAdminUsername/vmAdminPassword to virtualMachineAdminUsername/virtualMachineAdminPassword for improved clarity and consistency across modules.

Resource reference updates across dependent modules:

• Updated all resource references in dependent modules (such as storage accounts, private DNS zones, Key Vault, Cognitive Services, deployment scripts, machine learning workspace, and web sites) to use the new outputs from virtualNetwork instead of the old network module outputs, ensuring correct subnet and resource IDs are used for private networking. [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13]

These changes will make the infrastructure codebase easier to maintain and extend, and ensure that all resources are correctly provisioned and referenced when private networking is enabled.## Purpose

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Does this introduce a breaking change?

• Yes
• No

Golden Path Validation

• I have tested the primary workflows (the "golden path") to ensure they function correctly without errors.

Deployment Validation

• I have validated the deployment process successfully and all services are running as expected with this change.

What to Check

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