Adjust rails custom metrics generator to prefix filename with timestamp

We added a timestamp prefix to metrics yaml file definitions when importing all metrics form Event Dictionary.

The prefix is added in order to ensure the filenames are unique under a specific directory.

With this issue we add the timestamp prefix to the metric definition yaml file generator

Proposal:

Time.now.utc.strftime("%Y%m%d%H%M%S")}_#{file_name}.yml"