Allow to take screenshots from inside WhisperBack

It would be cool to be able to take a screenshot (of a region of the
screen maybe) from WhisperBack. Having a screenshot of the issues would
sometimes be more useful than a bad or incomplete description.

Related issues

Is duplicate of #8660

Original created by @sajolida on 7159 (Redmine)

To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information