[FEATURE] Expose file attachments/uploads to bot

[gpdeltedesco]

Is your feature request related to a problem? Please describe.
After the v12.31.4 release, along with the messaging v1.2.13 release adding the feature #646 (add attachments to core on teams), i was expecting to be able to get file attachments in my bots. This appears to be impossible right now.

Describe the solution you'd like
When an user sends attachments, i expect to receive the related metadata in incoming events (inside the event payload) and/or in incoming messages (in the message payload). I only expect the url, mime type and name, as collected (for Teams) in https://github.com/botpress/messaging/blob/020391d39b16056abad31687544a062dc91c16b1/packages/channels/src/teams/api.ts#L40.

I do not expect Botpress to automatically fetch the attachment and store it somewere, or to do any sort of processing.

Describe alternatives you've considered
To "hack" and somehow intercept requests to messaging webhook, and try to obtain the information from there.

Additional context
Adding attachments is a common request from our users... e.g: for sending screenshots to IT Support, or complementary data for creating a ticket.