more generic default params argument in get_task_id_params

[elray1]

Currently, the default value of the params argument to get_task_id_params is c("location", "horizon", "origin_date"), but those specific model task id variables are not relevant to all hubs. It may make sense for this function to be a method on a hub_connection object, and for it to do something like default to returning the first task id variable in the hub metadata file?