task-combined: add a fix to allow running nested launchers

This allows running launcher web and get the launcher to run the web entry of the procfile.

This enables us to set launcher as the command to run any other command on buildpack-based images, allowing us to run ad-hoc commands from the toolforge jobs run cli without having to manually specify launcher <mycommand>.

Bug: T355214 Signed-off-by: David Caro dcaro@wikimedia.org