Add endpoint that returns score based on number of builds running

I added it as metadata to the utilization_metrics endpoint
The proper way to use ```try``` is to call a method on a var that may be nil. In these two cases, it's being used improperly.

1. ```try(:project)``` - Using try here means you're not sure if the build you are calling it on is nil or not. But since you are calling it in a method within build, the build is indeed present for it to have gotten this far. Maybe the use you were trying for was to call ```try(:load_score)``` in the code where *load_score* was called on a possibly nil build.

2. ```try(:weight)``` - At first glance this seems sensible. What if the project is nil? But it might be argued that a build can't be created without a project. However, since there's no explicit validation, I'd say maybe you're a defensive coder, and this one is your call.