MAINTAINERS: Add niym-ot to Bluetooth Audio

Nithin has contributed the following PRs

https://github.com/zephyrproject-rtos/zephyr/pull/72908
https://github.com/zephyrproject-rtos/zephyr/pull/72333
https://github.com/zephyrproject-rtos/zephyr/pull/71798
https://github.com/zephyrproject-rtos/zephyr/pull/70373



and is attending the weekly LE Audio Zephyr meetings.

Signed-off-by: Lars Knudsen <larsgk@gmail.com>