Add migration instructions for platform transitions

[mheadd]

Overview

Add a new instruction file to help AI coding assistants support teams migrating applications to or from cloud.gov.

Proposal

See docs/MIGRATION-INSTRUCTIONS-PROPOSAL.md for the full proposal.

Benefits

• Broader utility for teams in transition, not just steady-state development
• Demonstrates that platform investment doesn't create barriers to future changes
• Creates natural extension point for community contributions
• Supports both inbound and outbound migration scenarios

Scope

Initial version should focus on:

• Outbound migration from cloud.gov (higher immediate value)
• Common targets: Kubernetes, AWS Fargate, Google Cloud Run
• Pattern detection over full automation

Implementation

Would create a new instruction file: .github/instructions/migration.instructions.md

This is a future enhancement - we'll prioritize based on community interest and feedback.

Related

• Platform-specific pattern detection (VCAP_SERVICES, CF environment variables)
• Concept mapping between Cloud Foundry and target platforms
• Migration artifact generation (Dockerfile, K8s configs)
• Compliance transition guidance