boards: st: nucleo_wb0*: start execution in bootloader

Nucleo-WB05KZ and Nucleo-WB09KE are lacking "--start-address" argument for
STM32CubeProgrammer runner, which makes them begin execution in limbo then
HardFault. On the other hand, Nucleo-WB07CC has it but starts execution
directly into user flash. This skips the bootloader code which performs
some bookkeeping (notably, updating RAM_VR.ResetReason); as a result,
code relying on RAM_VR.ResetReason is broken until PORRESET, or until
RESET occurs twice.

Force all three boards to begin execution in bootloader after flash to
ensure proper system behavior at all times.

Signed-off-by: Mathieu Choplain <mathieu.choplain@st.com>