Add support for `aspire do --list-steps` flag

[captainsafia]

When the flag is passed, we should print the steps that will be executed in the pipeline, their dependencies, and their tags, such as:

$ aspire do --list-steps
1. parameter-prompt
   └─ No dependencies

2. provision-redis-infra
   ├─ Depends on: parameter-prompt
   └─ Tags: provision-infra

3. provision-postgres-infra
   ├─ Depends on: parameter-prompt
   └─ Tags: provision-infra

4. build-webapi
   ├─ Depends on: parameter-prompt
   └─ Tags: build-compute

5. build-frontend
   ├─ Depends on: parameter-prompt
   └─ Tags: build-compute

6. deploy-webapi
   ├─ Depends on: provision-redis-infra, provision-postgres-infra, build-webapi
   └─ Tags: deploy-compute

7. deploy-frontend
   ├─ Depends on: build-frontend, deploy-webapi
   └─ Tags: deploy-compute

• Add a method to the IAppHostBackchannel interface on the AppHost side for getting the list of steps that will be displayed. Implement this API in the AppHostBackchannel.
• When the --list-steps flag is passed to the command, invoke the new method on the backchannel instead of running the activity logging loop. Stop the backchannel and app right away after printing the steps.

[davidfowl]

Hmmm not sure this should be just deploy, this should be part of PipelineCommandBase.

[captainsafia]

Yeah, I just saw the do PR and I think it should be part of that: aspire do --list-steps.

[christiannagel]

The flag --list-steps is not part of Aspire 13?
I'm using Aspire CLI 13.0.0+7512c2944094a58904b6c803aa824c4a4ce42e11.
With the flag --list-steps it tries to execute a step with that name.

[davidfowl]

aspire do diagnostics