Centralize user repo activity graph into Gitlab

Problem to solve

Our repo activity graph has become fragmented across 3 or more platforms after #MoveToGitlab

Further details

There is popular demand for an improved commit activity graph. https://gitlab.com/gitlab-org/gitlab-ce/issues/14078 With the success of Gitlab.com, CE and EE Repo activity has been fragmented away from Github, across many different domains. These graphs at the very least provide a valuable, easy to navigate personal record of activity that users value. According to the comments, many users have concerns about leaving GitHub because their activity would get fragmented.

Proposal

We could run a cron job to report github activity as "public commits" on one of our own repositories, call it commit-ledger. If this is successful, I can see it driving a number of people to switch, or at least not put up a fight when the business makes the proposal. This Commit Ledger could be used to harvest activity from private CE/EE installations as well with a service account.

What does success look like, and how can we measure that?

Success maybe be measured by seeing an increase of over ~10% in Github account linkages to get this feature enabled. Granted it's hard to measure how much people love the graph.

Links / references

https://gitlab.com/gitlab-org/gitlab-ce/issues/14078#note_94099655