Make GPT available in the GDK via gdk measure command or a new one

Summary

The first step of Make passing GitLab Performance Tool results a ... (&150) is to make GPT available via a command in GDK.

Steps

• Figure out how to add a GDK command -- we can probably model it off of gdk measure, which uses a container to run sitespeed.
• Do we need any configuration for GPT stored?

Success Criteria

• Can run GPT test against GDK from a GDK command