[WIP] feat: aspire exec command support

[DeagleGross]

Note: work in progress

Description

The idea is to have a separate aspire exec cli command, which allows to execute a command against some resource. It is the first part of Entity Framework E2E scenario improvements.

Contract: aspire exec --resource <targetResource> --command <command>.
Parameters:

• resource specifies which resource command should target. In case target resource is csproj, then in which working directory should command be executed.
• command specifies which command to execute. In case of EF it can be dotnet ef migrations add Initial.

Implementation

Aspire exec does the following under the hood:

1. parses the input from Aspire.cli side, and runs (in "run" mode) the AppHost with --operation exec argument. This is a new type of DistributedApplicationOperation.
2. DistributedApplication starts normally, except it tries to find the target resource, and only starts it and its dependencies. Consider this apphost:

var miniPostgres = builder.AddPostgres("miniPostgres");
var postgres = builder.AddPostgres("postgres");

// target resource
var webAppProject = builder.AddProject<TestingAppHost1_MyWebApp>("mywebapp1")
    .WithReference(postgres);

var workerProject = builder.AddProject<TestingAppHost1_MyWorker>("myworker");

If "mywebapp1" is the target resource, then only "mywebapp1" and "postgres" will start (not "miniPostgres" or "myworker").

3. As a AfterResourcesCreatedAsync lifecycle hook I've attached Aspire.Hosting.Exec.DefaultCommandExecutor - all it does it parses the command, and executes it against the target resource.

4. Maybe we need to forcefully shutdown apphost here?

TODO

• attach the IAppHostBackchannel to see the logs and status of execution
• test e2e from Aspire.Cli
• prettify code / catch exceptions etc

Checklist

• Is this feature complete?
  • Yes. Ready to ship.
  • No. Follow-up changes expected.
• Are you including unit tests for the changes and scenario tests if relevant?
  • Yes
  • No
• Did you add public API?
  • Yes
    • If yes, did you have an API Review for it?
      • Yes
      • No
    • Did you add <remarks /> and <code /> elements on your triple slash comments?
      • Yes
      • No
  • No
• Does the change make any security assumptions or guarantees?
  • Yes
    • If yes, have you done a threat model and had a security review?
      • Yes
      • No
  • No
• Does the change require an update in our Aspire docs?
  • Yes
    • Link to aspire-docs issue (consider using one of the following templates):
      • New (or update) doc-idea template
      • New breaking-change template
      • New diagnostic template
  • No

Relates #9859

[DeagleGross]

dropped in favor of #10240