Feature request: showing % of contributions coming from within an org vs. outside

It's similar to the current Collaboration chart, except instead of visualizing _which_ orgs collaborate with each other, I would like to be able to track what % of contributions come from outside the org (vs. inside), for some definition of "contribution". One idea: number of commits in master authored by members of the organization, vs. number of commits by non-members of the org? I'm open to different definitions.

I would love for this to be time-series data, that is, tracking this % of outside contributions over time. This is similar to #35 in that slicing the data up by time would be required.

Finally, one extension of this could be doing a similar analysis except replacing 'org' with 'repo'.

Let me know what you think. I'm happy to take a stab at this, but I'm still learning the project 😓. Haven't delved into the `updater/` portion of the repo yet, which is where I believe this change would need to land.

Start by reading the updater/ portion of the repository and the existing Collaboration chart, then trace how contribution data is collected and sliced by time. Before implementation, clarify the definition of contribution and whether the scope includes organizations, repositories, or both; done requires an agreed metric and time-series percentage view.

Written by the indexing model from the issue text.