fix: added dns for existing project to access

[AjitPadhi-Microsoft]

Purpose

• This pull request introduces several infrastructure improvements and refactors, primarily focusing on Azure resource management, parameter naming consistency, and script reliability. The most significant changes are grouped below:

Azure Resource Provisioning and Networking

• Added conditional creation of a private endpoint for existing AI services when both useExistingAiFoundryAiProject and enablePrivateNetworking are enabled, ensuring secure and isolated network access for these resources (infra/main.bicep).
• Simplified the logic for provisioning private DNS zones by removing the exclusion of AI-related DNS zone indices, now provisioning all zones when private networking is enabled (infra/main.bicep).

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

Verify that the following are valid

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