Provide a way to list the available project resources without starting up everything to help product owners discover them

Describe the Feature You Want

I would love to see a command like:

> tilt list
backend
frontend
storybook
database
db-ui
frontend-test

# or
> tilt list-resources
backend
frontend
storybook
database
db-ui
frontend-test

That allows a user to discover the available resources without having to run tilt up and already consuming the necessary CPU, RAM, ... just to see the available service names that could be started separately.

Current Behavior

Currently, we recommend our product managers to:

• use tilt up and read the names in the web ui
• scroll through the Tiltfile and use everything that has name="..."

Why Do You Want This?

We've recently introduced Tilt to help new developers onboard quicker and unify development environmentes. We've also introduced it to allows product owners to test PRs more quickly.

The proposal would be especially helpful for our product owners/project managers that lack the technical skill to read the Tiltfile and sometimes work on resource constrained machines. It would also help our developers (although to a lesser extend, as they are able to read Tiltfiles more easily).

Additional context

I've searched through the github issues and the documentation but was not able to find this feature. It surprised me that this does not exist, so I'm thinking that it is rather me who missed something than the feature actually not being available.

Thanks for building Tilt - we soon want to introduce it everywhere as initial feedback from both devs and PMs has been great!

Start with the proposed tilt list or tilt list-resources CLI entry point and compare it with the current tilt up workflow described in the issue. Done means the command lists resources such as backend and frontend without starting services or consuming runtime resources.