#### Is your feature request related to a problem? Please describe.
No.

#### Describe the solution you'd like
#4734 Changed the entire behavior of the params serializer, breaking using any custom functionality on the consumer side. Add a boolean switch to mimic pre 1.x behavior (default is false) and send the params directly to the encode function

#### Describe alternatives you've considered
Tried working with new solution; it did not pan out well and led to more bugs with our requests

lib/helpers/buildURL.js
if (!params) {
    return url;
  }
  const hashmarkIndex = url.indexOf('#');
  if (hashmarkIndex !== -1) {
    url = url.slice(0, hashmarkIndex);
  }
  const _encode = options && options.encode || encode;
  const serializeFn = options && options.serialize;
  let serializedParams;
  if (serializeFn) {
    serializedParams = serializeFn(params, options);
  } else {
    serializedParams = utils.isURLSearchParams(params) ?
      params.toString() :
      new AxiosURLSearchParams(params, options).toString(_encode);
  }
  if (serializedParams) {
    url += (url.indexOf('?') === -1 ? '?' : '&') + serializedParams;
  }
  return url;
}