Update "maintainers" and "alumni" GitHub teams

[scottrigby]

Depends on:

• Add more alumni to maintainer emeritus section #124

to-do:

• Ensure @open-gitops/maintainers reflects https://github.com/open-gitops/project/blob/main/MAINTAINERS
• Ensure @open-gitops/alumni reflects https://github.com/open-gitops/project/blob/main/MAINTAINERS Emeritus section