As far as I know, there isn't a way to add emojis in the text with the options in workspace. Sometimes if you copy and paste the emoji from another source, it will work. But it doesn't always. If you really wanted to have an emoji, you could save it as an image and link to the image, as that is possible in workspace. Though currently the image has to be hosted online somewhere and linked to it, it can't just be uploaded into the workspace.
