POST/GET Launching

### Proposed change
Not sure if this is already implemented, but is there a method to specify launch variables like req_queue and such in a POST or GET request on the spawner page (ie. instead of using wrap spawner)?

### Who would use this feature?
I'd like to design an external form to then send POST or GET to jupyterlab. I'd like the form to be external because the form needs to change depending on the user logged in and such.