GCB builder may exhaust `get` quota with large number of build artifacts

GCB has a quota of 660req/min on `get`s to check build results. When dealing with builds with many artifacts, with a larger team, it's not impossible to hit this threshold.

We currently have [an exponential backoff](https://github.com/GoogleContainerTools/skaffold/blob/ff5038a51e8408e5ac80f66b6867ff2b4ba528c2/pkg/skaffold/build/gcb/types.go#L71-L78) that starts at 1s and increases by 1.5x per step to a maximum of 10 steps with a cap of 60s. That means we could check 8 times per minute per container. With 15 containers in the project, that could be hit if 5 people are building simultaneously (e.g., incl CI builds).

GCB supports a [`list` operation](https://cloud.google.com/build/docs/api/reference/rest/v1/projects.builds/list) that takes a filter. We should be able to use this operation for the suite of builds that have been created and reduce our API use.