[Recommended] Enhance Maintainer Lifecycle Documentation

[kfaseela]

Hello OpenFGA Community,

As part of OpenFGA Incubation request, the CNCF TOC has noted down some improvement suggestions that would be beneficial for the OpenFGA community in the long term and would eventually be useful at the time of Graduation.

While the maintainers have been documented at https://github.com/openfga/community/blob/main/MAINTAINERS.md, there is still scope for improvement to define and demonstrate onboarding, offboarding, and emeritus processes of the maintainer lifecycle. Also please demonstrate usage of the maintainer lifecycle with outcomes, either through the addition or replacement of maintainers as project events have required.