Revise PLEP 2 on PlasmaPy governance

[namurphy]

PLEP 2 defines PlasmaPy's governance policies and practices. However, PLEP 2 was written in 2017 and last revised in 2018, when the project was significantly younger. We should revise PLEP 2 to better reflect our current practices.

We can also learn from related projects who have revamped their governance policies and practices, like Astropy in 2021 (where they defined Voting Members) and SunPy in 2024 (where they defined Project Custodians).

It would be worthwhile to do this around the same time as applying to become a sponsored project of NumFOCUS. 🌱 NumFOCUS isn't accepting applications at the moment because they've gotten a lot of applications, and possibly also because they've been going through changes as an organization. Their next update from NumFOCUS about this should be in mid-2026.

[namurphy]

One of the changes I'd like is to make it so that anyone who is working on PlasmaPy full time for more than a few months to get added to the Coordinating Committee for a three year term.