Maybe this is the missing piece?
Update: never mind, your config.toml probably already looks like this, otherwise it wouldn’t be able to schedule service task that use a gpu.
Update2:
I just noticed now that you already shared the relevant line from your config.toml:
Apparently what follows the prefix DOCKER_RESOURCE_ is what needs to be the key of the entries in node-generic-ressource in the daemon.json and the value for kind in discrete_resource_spec