`local` run-once option for `tilt up`

Describe the Feature You Want

local run once or some prerequisite phase that runs only once for a tiltfile.

Current Behavior

Tilt tries to generate files that trigger the k8s_yaml or any deps field change and reload of tilt. This leads to an endless loop of local commands triggering k8s_yaml tilt reload. I don't want to ignore the files as these are regenerated with each save by a tilt state.

Why Do You Want This?

This phase can be used to pre-generate some files that will be loaded as resources by k8s_yaml without triggering an endless loop. I use kapitan go generate some files and would like to generate the files for each save. But to load these files in the first place I have to have them in the folder which requires me to do the first generation outside of Tilt.

Additional context
Add any other context or screenshots about the feature request here.

Start by tracing the tilt up handling of local commands, k8s_yaml, and deps changes. Reproduce the regeneration loop described in the issue, then define the run-once behavior and verify that prerequisite generation does not trigger an endless reload while later saves still regenerate the files.