MAINTAINERS: Add jthm-ot to Bluetooth Audio

Jens has contributed the following PRs

https://github.com/zephyrproject-rtos/zephyr/pull/68678
https://github.com/zephyrproject-rtos/zephyr/pull/72409
https://github.com/zephyrproject-rtos/zephyr/pull/72915
https://github.com/zephyrproject-rtos/zephyr/pull/73564
https://github.com/zephyrproject-rtos/zephyr/pull/73656



and is attending the weekly LE Audio Zephyr meetings.

Signed-off-by: Lars Knudsen <LAKD@Demant.com>