Maintainers.txt: Add new reviewer for UefiPayloadPkg

Maintainers.txt: Add new reviewer for UefiPayloadPkg

Add Sean Rhodes as UefiPayload reviewer mainly focus on
UEFI payload for coreboot support.

Signed-off-by: Guo Dong <guo.dong@intel.com>
Cc: Ray Ni <ray.ni@intel.com>
Cc: Benjamin You <benjamin.you@intel.com>
Cc: Maurice Ma <maurice.ma@intel.com>
Cc: Michael D Kinney <michael.d.kinney@intel.com>
Cc: Sean Rhodes <sean@starlabs.systems>
Reviewed-by: Ray Ni <ray.ni@intel.com>
Reviewed-by: Sean Rhodes <sean@starlabs.systems>