[What's New Analysis] Create aspire do pipelines documentation

Summary

Aspire 13.0 introduced aspire do pipelines as the replacement for publishing callbacks. This is only documented in what's-new, with no standalone reference.

What's Missing

Core Concepts

// Old way (deprecated)
.WithPublishingCallback(async (context, ct) => { ... });

// New way
.WithPipelineStepFactory(context => {
    return new PipelineStep() {
        Name = "CustomDeployStep",
        Action = CustomDeployAsync,
        RequiredBySteps = [WellKnownPipelineSteps.Publish]
    };
});

CLI Commands

aspire do              # Run default pipeline
aspire do build        # Run build step
aspire do push         # Push to container registry
aspire do deploy       # Deploy to target
aspire do deploy-api   # Run specific named step

WellKnownPipelineSteps

• Build / Publish / Deploy - standard steps
• Custom step registration and dependencies

Suggested Content

1. What is aspire do - Pipeline concept overview
2. Built-in steps - build, push, publish, deploy
3. Running specific steps - aspire do <step-name>
4. Custom pipeline steps - PipelineStep, dependencies, RequiredBySteps
5. Migration guide - From WithPublishingCallback to WithPipelineStepFactory
6. Examples - Multi-environment deploys, custom build steps

Why It Matters

Publishing callbacks are deprecated. Users upgrading from 9.x need migration guidance, and the pipeline system is central to deployment.