[feature] experimental for CSV request

[dawadam]

Hi, thanks for this great job. Experimental function make error with CSV result :

I try with :

alpha.experimental('LISTING_STATUS')

Error is :

FetchError: invalid json response body at https://www.alphavantage.co/query?apikey=XXX&function=LISTING_STATUS reason: Unexpected token s in JSON at position 0
    at /node_modules/cross-fetch/node_modules/node-fetch/lib/index.js:273:32
    at processTicksAndRejections (node:internal/process/task_queues:95:5) {
  type: 'invalid-json'
}