Add ability to upload multiple images at a time for a post/comment

[hjiangsu]

Pull Request Description

This PR adds the ability to upload multiple images at once to a given post/comment body. When uploading an image as a link, it will be restricted to only a single image.

Issue Being Fixed

Issue Number: N/A, but possibly fulfills the following post: https://lemmy.world/post/17335550

Screenshots / Recordings

Multi-image upload for posts:

multi-image-upload-post.mp4

Multi-image upload for comments:

multi-image-upload-comments.mp4

Checklist

• If a new package was added, did you ensure it uses an appropriate license and is actively maintained?
• Did you use localized strings (and added appropriate descriptions) where applicable?
• Did you add semanticLabels where applicable for accessibility?

[micahmo]

Nice!