fix(task): support tasks without commands

[marvinhagemeister]

Support running tasks that have no command and only dependencies. This is useful for when you want to group tasks only.

• Depends on feat(task): support optional command deno_config#144

Fixes #27165

[bartlomieju]

Marking as "Request changes" so we don't land it by accident before v2.2 merge window.

[bartlomieju]

Can you update the description to mention that this field is required unless there's "dependencies" field specified?

[marvinhagemeister]

Is it required though? Having a task like this is valid in the string form:

{
  "tasks": {
    "foo": ""
  }
}

And I guess the same is also fine for the object notation:

{
  "tasks": {
    "foo":  {}
  }
}

That's just a task that does nothing.

[dsherret]

LGTM. Kind of feels like we could just merge this as a fix.

[bartlomieju]

I'm fine merging it as a fix. Please update docs before merging it though