Automatically start service on WSL on Windows:
First configure it to start the service without asking a password.
Create line in /etc/sudoers.d/ (at WSL to prevent asking password):
%sudo ALL=(ALL) NOPASSWD: /usr/sbin/service xrdp *
Create .bat file in Windows startup directory with for example the following lines:
wsl sudo service dbus start
wsl sudo service xrdp start