update contributors page

[samumantha]

[https://coderefinery.org/about/contributors/])
-> check instructors and group by CR workshop and other workshops

[samumantha]

Suggestion:
Move previous contributors to "partners page" (new section). Add special thanks to people that contributed a lot.
Add general shoutout to all helpers and instructors, but keep them only on "past workshops" pages?

@bast

[samumantha]

In addition: add ambassadors