Use auth file instead of creds in quadlet files

roles/service/meta/argument_specs.yaml

@@ -66,22 +66,6 @@ argument_specs:
         description: "The image to run in the service container(s), in FQIN format (registry/imagename:tag)."
         type: str
         required: true
-      service_container_image_creds:
-        description: Credentials used to authenticate with the registry
-        type: dict
-        required: false
-        default:
-          username: ""
-          password: ""
-        options:
-          username:
-            description: Username
-            type: str
-            required: true
-          password:
-            description: Password
-            type: str
-            required: true
 
       service_container_user:
         description: The UID to run as inside the container