Attachments aren't showing up as interactive message buttons

[m23tran]

SlackAttachmentAction has the type property exposed so attachments can appear as buttons.

Attachment doesn't seem to have that property exposes or set it at all.

[Workshop2]

I will have to look into synchronising the noobot object with the slack library. I probably won't have time during the week, so if you can wait I can get to it. Alternatively feel free to send a PR