refactor: separate search service module to enable managed identity to reduce deployment time

[Harsh-Microsoft]

Purpose

This pull request introduces significant improvements to the deployment of Azure Cognitive Search services within the infra/main.bicep file. The changes focus on enhancing configuration flexibility, improving security, and optimizing deployment time by separating managed identity enablement into a distinct module.

Enhancements to Azure Cognitive Search deployment:

• Added comprehensive parameterization to the avmSearchSearchServices module, including telemetry, monitoring, SKU selection, role assignments, semantic search, and private networking options.
• Introduced conditional configuration for private endpoints and public network access, supporting secure and scalable deployments.

Security and role management:

• Defined explicit role assignments for the search service, granting both contributor and reader roles to a user-assigned managed identity.

Deployment optimization:

• Created a separate avmSearchSearchServicesEnableIdentity module to enable managed identity, reducing overall deployment time.
• Added a dependsOn clause to ensure proper sequencing between the main search service and the identity module.

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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