Metric: time to clone repos on cloud

Created by: ebrodymoore

From @quinnkeast here:

I'd still love to know:

how long it takes to clone all the repos added / average time depending on the number of repos

As it will influence the post-signup flow in the future.

We don't capture this right now AFAIK so I'll leave it to @sourcegraph/cloud-saas to prioritize with @quinnkeast. Let us (@attfarhan and I) know if any help is needed!