Chunked media upload example

[lyzadanger]

Hello! This PR adds a multi-step chunked media upload example.

[desmondmorris]

@lyzadanger this is great! Thanks for the contribution!

[ashatat]

@lyzadanger @desmondmorris
I am stuck on this
I see in this example you send the file in one chunk, what if there was more than one?
I tried it and I got HTTP Error: 400 Bad Request

here is my code:

const streamFile = fs.createReadStream(file.path, { highWaterMark: 1024 * 1024 });
      function makePost(endpoint, params) {
        return new Promise((resolve, reject) => {
          client.post(endpoint, params, (error, data, response) => {
            if (error) {
              console.log(error)
              reject(error);
            } else {
              resolve(data);
            }
          });
        });
      }
      makePost('media/upload', {
        command: 'INIT',
        total_bytes: file.size,
        media_type: file.mimetype,
      })
        .then((data) => {
          console.log('INIT', data);
          let counter = 0;
          streamFile.on('data', async (chunk) => {
            console.log('counter', counter);
            console.log('chunk', data.media_id_string);
            makePost('media/upload', {
              command: 'APPEND',
              media_id: data.media_id_string,
              media: chunk,
              segment_index: counter,
            }).then(appendData => console.log('APPEND', appendData));
            counter += 1;
          });
          streamFile.on('end', () => {
            makePost('media/upload', {
              command: 'FINALIZE',
              media_id: data.media_id_string,
            })
              .then(result => console.log(result)).catch(error => console.log(error));
          });
        });

what I am missing?