docs: update code sample

[jstirnaman]

    ```suggestion
    btoa('EMAIL_ADDRESS:PASSWORD')

Replace with `btoa` with Node `Buffer`.

_Originally posted by @jstirnaman in https://github.com/influxdata/openapi/pull/580#discussion_r1004710632_
      

[EstherChristopher]

Hi @jstirnaman, can you also provide a link to this issue?