[tf-rmm] Welcoming Raghu as TF-RMM maintainer

Hi Everyone, I'm pleased to announce that Raghupathy K has joined the group of maintainers for TF-RMM. This decision reflects Raghu's significant contributions to the project, including code reviews, design discussions and feature contributions over the past couple of years.

The maintainers file has been updated accordingly : https://github.com/TF-RMM/tf-rmm/blob/main/docs/about/maintainers.rst

Best regards, Soby Mathew (on behalf of all TF-RMM maintainers)