Add Docker Compose migration guide

[Copilot]

This PR adds a comprehensive migration guide to help developers transition from Docker Compose to .NET Aspire. The guide addresses the issue raised in #936 where many people are trying to migrate from Docker Compose to .NET Aspire but lack guidance on how concepts translate between the two systems.

What's included

The new guide (docs/get-started/migrate-from-docker-compose.md) covers:

• Conceptual differences between Docker Compose and .NET Aspire
• Practical migration examples for common scenarios:
  • Multi-service web applications
  • Container-based services
  • Environment variables and configuration
  • Custom networks and volumes
• Step-by-step migration strategy
• Docker Compose publishing capabilities introduced in .NET Aspire 9.3
• Troubleshooting tips and community resources

Example migration

The guide shows how to convert typical Docker Compose setups:

Docker Compose:

services:
  api:
    build: ./api
    depends_on:
      - database
  database:
    image: postgres:15
    environment:
      - POSTGRES_DB=myapp

.NET Aspire equivalent:

var builder = DistributedApplication.CreateBuilder(args);

var database = builder.AddPostgres("postgres")
    .WithEnvironment("POSTGRES_DB", "myapp")
    .AddDatabase("myapp");

var api = builder.AddProject<Projects.MyApp_Api>("api")
    .WithReference(database);

builder.Build().Run();

Changes made

• Added new migration guide at docs/get-started/migrate-from-docker-compose.md
• Updated docs/toc.yml to include the guide in the Get Started section with appropriate display keywords
• All markdown formatting follows repository guidelines and passes linting

The guide is positioned in the "Get Started" section as it helps developers new to .NET Aspire understand how to transition from their existing Docker Compose workflows.

Fixes #936.

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Internal previews

📄 File	🔗 Preview link
docs/get-started/migrate-from-docker-compose.md	docs/get-started/migrate-from-docker-compose
docs/toc.yml	docs/toc