Actually wait a minute. Since we are already forwarding remaining arguments through to the command to start the DevTools server, I don't think we need to parse this manually from the serve command. Try passing the --dtd-uri flag to the serve command without this change.

@kenzieschmoll without this change i got the following error:

So I figured that adding it here was kind of like allowlisting it

I think we do need this for the same reasons we have things like --allow-embed and --machine. The current arg parser allows for additional arguments, but not additional options/flags (unless we use AllowAnythingParser). (see discussion in #6670)