Add support for user-defined autotype tool

[bitwarden48684]

Hi there, thanks for making this tool, I find it very useful.

Is there any chance that the AUTOTYPE_MODE variable can be set via an environment variable?

My setup uses ydotool, but without using sudo, and thus bwmenu autotype does not work (as it requests the sudo password). Perhaps with the following patch, users could set their own typing tools.

# Stores which command will be used to emulate keyboard type
-AUTOTYPE_MODE=
+AUTOTYPE_MODE=$BWMENU_AUTOTYPE_MODE