twister: Allow baud rates other than 115200

Fixes #38046
Document the changes in twister.rst
Add baud rate to debug message in twister
Add baud parameter to twister's add_device function
Set the twister baud rate from input parameters
Use 115200 as the default baud rate if not specified
Add baud to the hwmap-schema.yaml file
Add --device-serial-baud to twister arguments
Fix compliance issues
Fix mistake in parameter name from device-baud to device-serial-baud
Refactoring of the code in orded to simplify the logic
   and clear multiple definitions of the default baud rate.

Signed-off-by: Maciej Perkowski <Maciej.Perkowski@nordicsemi.no>
Signed-off-by: Dennis Ruffer <daruffer@gmail.com>