boards: nordic: nrf54h20pdk: add debugging support using J-Link

cpuapp/cpurad can be debugged using the J-Link runner.

Note:
This feature is still experimental and has known issues. For example,
setting a breakpoint to main requires to patch init.c with a loop
polling a variable so that we stop there until unset from GDB.

Signed-off-by: Gerard Marull-Paretas <gerard@teslabs.com>