docs: add a GOVERNANCE.md

[Ayushmore1214]

What would you like to be added: A simple GOVERNANCE.md that explains the roles in the project (contributor, member, approver, maintainer), how to get each one, and how decisions are made.

Why is this needed: Right now info about roles is spread across MAINTAINERS.md, CONTRIBUTING.md and CODEOWNERS, and it's not written anywhere how someone becomes an org member or maintainer. Having it in one place would help new contributors and the contributor ladder (#7383)

For reference:

• Backstage: https://github.com/backstage/community/blob/main/GOVERNANCE.md
• Meshery: https://github.com/meshery/meshery/blob/master/GOVERNANCE.md