Add support for attachments

[clembou]

We need to find a way for users to upload screenshots that will be uploaded somewhere and accessible from github.

We could either add them as images in markdown in the body of requests once the screenshots have been uploaded, or just add a formatted link at the bottom of user requests pointing to the uploaded images.

Azure storage seems like the obvious option but there may be alternatives. The content of the screenshot is sensitive so the chosen solution will need to be secure and files should have restricted access.