samples: boards: nrf: Add nrf2_clock_control sample

Add a sample that presents how the custom nrf2_clock_control API
introduced for nRF54H20 can be used for the various clocks which
are supported by it.

Signed-off-by: Andrzej Głąbek <andrzej.glabek@nordicsemi.no>
Signed-off-by: Bjarki Arge Andreasen <bjarki.andreasen@nordicsemi.no>