Add option to select thumbnail quality

[hjiangsu]

Pull Request Description

This introduces a new option in Appearance -> Posts -> Feed Settings to choose the thumbnail quality for thumbnails hosted on Lemmy instances (using pictrs). When the quality is selected, it will request a smaller size from pictrs. This setting applies to both compact and card modes.

This option should help with some data reductions (alongside not showing thumbnails at all). One thing to note is that this currently also affects the image viewer (since it uses the same url for both thumbnails and viewer). I'd like to make it an option to view the full resolution image first before marking this PR as ready.

Issue Being Fixed

Issue Number: N/A

Screenshots / Recordings

Checklist

• [ ] Did you update CHANGELOG.md?
• [ ] Did you use localized strings where applicable?
• [ ] Did you add semanticLabels where applicable for accessibility?