Add images and attachments in Conversations / Groups

Is your feature request related to a problem? Please describe.

Conversations and Decidim Groups is an interesting feature, but very minimalistic and scarcely used. It could be more relevant as "messenger" equivalent and support interaction between participants, if the possibility of image / attachment uploads was given.

Describe the solution you'd like
Image / Attachment Upload in Conversations.

Describe alternatives you've considered
None

Additional context
We are developing a feature to make Decidim more suitable for Community-management in local neighbourhoods - that's when we discovered that "Conversations" had more potential.

Does this issue could impact on users private data?
Not that I'm aware of.

Funded by
Funding available via DIGIgrätzl Project by digifonds/Arbeiterkammer Wien.