Add Ramkumar as a maintainer

[sudo-bmitch]

I'm nominating @rchincha as a maintainer. He's been instrumental in the 1.1.0 release, including contributions to the conformance tests and a key contributor to the Zot registry we use for testing.

This change requires approval from 6 maintainers.

[jzelinskie]

I'm supportive of a reviewer or emeritus for those that are inactive, but still have important historical knowledge or opinions. However, I also think it's unfair to block those that have been putting in the effort from becoming maintainers until that issue has been resolved.