Expose Attachment filenames in Dynamic Variables

It would be useful to access a list of Attachment filenames (on Messages and/or Conversations) when working with Dynamic variables in Rules.

One application of this could be;

1. Scan attachment filenames to see if they match the pattern of my Stripe Invoices (such as Invoice-{letters}-{numbers}.pdf)

2. Extract this Invoice number, and Send an Application Request/Object calls to the Stripe API to pull live Invoice and attach it to the conversation.