[CBBS] Run go generate on pre-commit hook

What is the problem?

We now autogenerate metrics and their metadata with the script in generation/generate_metrics.go. This is helpful but you need to remember to run the script if you modify the metrics.

What is the solution?

We should run go generate on the pre-commit hook if statistician/statistician.go, statistician/metrics.go or generation/generate_metrics.go are in the staging area and then autoformat the resulting generation/metrics.generated.go file.