Fail branch label computation for history view gracefully (BB-11563)

We're failing to bail out early and serve the history node page for individual files because of a timeout computing the DAG, when we should just show the page without the grey branch labels for repositories with thousands of refs.

We've created an internal issue to start by capping the amount of time we are willing to burn on computing this data synchronously at request time and just serve the page without the labels if we exceed that.