Add the second-time contribution metric

[InessaPawson]

Besides monitoring some community health metrics from the CHAOSS list (https://chaoss.community/kb-metrics-and-metrics-models/), I’ve set a second contribution as the north star for NumPy to measure our efforts in creating a welcoming to newcomers culture.

Currently, I’m monitoring second contributions to numpy/numpy manually via GitHub projects. (Refer to NumPy first-time contributor PRs.) It would be very helpful to automate this process.

Two options emerged during discussions with the NumPy maintainers:
– introducing a bot,
– adding the metric to the devstats dashboard.
Avoiding a bot is preferred by the NumPy team, hence this request.