Hi, are you planning someone from them to implement? It would be very great! Thanks in advance.
If you use the latest available version of Vaultwarden it is already there.
You probably have to click on “Benutzername”.
Compare the previous images you posted. The first one has “Username” selected, the second (in german) does not. So you have to select “Benutzername” there. 
The first is from the web: Username & Password Generator | Bitwarden Hilfe-Center
The other printscreens are from my vaultwarden.
