Add support for any file type in attachments (image picker button)

[MechDR]

Requirements

• [X] This is a feature request and not a bug report. Otherwise, please create a new bug report instead.
• [X] Please check to see if this request (or a similar one) already exists.
• [X] It's a single feature. Please don't request multiple features in one issue.

Describe the feature you'd like

Basically, the title. This will make Lemmy a viable alternative for a dying breed of platforms - forums. I run an electronics forum and we exchange a lot of different mime/file types, not just images.

It would at least be nice to have a config somewhere in the settings that lets you change the image upload icon with a general attachment (paperclip) icon and sets the UI to not get picky about mime types (anything is allowed). Of course, the default should be images.

[RokeJulianLockhart]

@MechDR, have you tried Discourse?