Add GraphQL Mutations + Subscriptions support for GovCloud version

[sindhu-achuthan]

Describe the solution you'd like

We need a containerized GraphQL service that can replace AppSync for FedRAMP High/GovCloud deployments. The solution should:

1. Expose GraphQL API - Support mutations (uploadDocument), queries (getDocument), and subscriptions (onUpdateDocument)
2. Run in containers - Deploy behind ALB for FedRAMP High compliance instead of using AppSync
3. Maintain existing workflow - Customer calls uploadDocument → gets presigned S3 URL → uploads file → receives completion notification via
   subscription
4. Enable on-premises integration - Allow external applications to integrate directly with the document processing pipeline through GraphQL API

The customer workflow would remain identical:
• Call uploadDocument mutation to get presigned POST URL
• Upload file directly to S3 using presigned URL
• Subscribe to onUpdateDocument to receive processing completion events
• Fetch results using getDocument or similar queries

Describe alternatives you've considered

Post-processing Lambda hook - Won't work because the on-premises application needs bidirectional API communication. They can't easily integrate with S3 buckets and event-driven AWS components directly from their environment.

Custom API layer - Customer would have to build a separate interface layer and handle authentication, authorization, and API design from scratch, significantly increasing complexity and development time.

Additional context

• Environment: AWS GovCloud with FedRAMP High requirements
• Usage: Headless/API-only (no UI needed)
• Integration: On-premises applications need GraphQL API access
• Compliance: AppSync is not FedRAMP High certified, blocking current deployment
• Architecture: Need containerized GraphQL service behind ALB instead of managed AppSync