scripts: requirements: extras: add zcbor
scripts: requirements: extras: add zcbor

Add ZCBOR to the requirements-extras.txt and require at least version
0.6.0 which is the current version of the ZCBOR C library.

Signed-off-by: Veijo Pesonen <cb89a3750227d52d34160f03c031368aef19d3be@nordicsemi.no>

zephyrproject-rtos/zephyr,zephyrproject-rtos/zephyr,zephyrproject-rtos/zephyr,zephyrproject-rtos/zephyr,zephyrproject-rtos/zephyr