Source Asana: new stream Attachment

[ycherniaiev]

Tell us about the problem you're trying to solve

An attachment object represents any file attached to a task in Asana, whether it’s an uploaded file or one associated via a third-party service such as Dropbox or Google Drive.

Describe the solution you’d like

Research pros and cons for implemting this stream.
Depending on your role within Asana you may see not all attachements:

[topefolorunso]

I will work on this @justinbchau, please assign it to me. I've raised PRs for other issues