Protect resources from deletion during a force update

[wendorf]

Describe the Feature You Want

Adding a tilt.dev/force-update-policy=keep annotation to a Kubernetes resource prevents Tilt from deleting the resource during a force update

Current Behavior

A force update will attempt to delete all managed Kubernetes resources, even those with tilt.dev/down-policy=keep.

Why Do You Want This?

I use Tilt to manage CustomResourceDefinitions. For example's sake, let's say with kind: Pizza. The application that I'm deploying with Tilt creates new Pizzas at runtime. When I trigger/restart the Tilt resource, it deletes the Pizza CRD, which causes Kubernetes to also delete all Pizzas.. This is disruptive, since Tilt is not managing the Pizzas themselves so won't recreate them, and my application state becomes inconsistent.

If I could tell Tilt to not delete my CRD during a force update, then my application's state could stay consistent.

Additional context
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