determine how long it took between when a resource started running and when it became ready

Describe the Feature You Want

Currently, Tilt publishes APIs to help you determine how long a local server has been running:
https://api.tilt.dev/core/cmd-v1alpha1.html

There's also an API to determine the current readiness state:
https://api.tilt.dev/interface/ui-resource-v1alpha1.html

But there's currently no API to help you figure out how long the resource took to become ready.

Additional context

This overlaps with a bunch of other things we're working on right now, including:

• The ability to have CLI tools that wait until a resource is ready (https://github.com/tilt-dev/tilt/issues/5092)
• Porting resource_deps over to the API (which presumably would wait on a condition)

I think the right short-term way to do this would be to add a few metav1.Condition objects to UIResource:
https://pkg.go.dev/k8s.io/apimachinery/pkg/apis/meta/v1#Condition

In particular, we could have a "Ready" condition (for when a UIResource becomes ready) and a "Started" condition (for when a resource is first deployed / first starts running)

Start by reading the UIResource API documentation and the metav1.Condition definition referenced in the issue, then inspect how current resource readiness and running state are exposed. Done means the API exposes Started and Ready conditions for a UIResource so callers can determine the time between deployment or startup and readiness, with the interaction with waiting and resource dependencies understood.