boards: olimex_lora_stm32wl_devkit: Support newer board revisions

Add configuration and DT overlays for new devkit revisions C and D.

This enables identical behavior to earlier revisions by powering the VDDIO
pins on the UEXT1 connector and CON1 header via the new FET2 regulator.
In these new revisons this regulator is also user-togglable.

Update documentation build/flash/debug steps.

Signed-off-by: Kenneth J. Miller <ken@miller.ec>