add low-bandwidth mode

[KiaraGrouwstra]

Pre-Flight checklist

• Did you check to see if this issue already exists?
• This is a single feature request. (Do not put multiple feature requests in one issue)
• This is not a question or discussion. (Use https://lemmy.ml/c/jerboa for that)

Describe The Feature Request Below

jerboa's list view currently eagerly loads links' preview images.
on metered connections, it may be desirable to disable this so as to conserve bandwidth.
as such, it would be nice to see such a low-bandwidth mode added to jerboa.

c.f. #584 which mentioned this consideration as well

[MV-GH]

related #716

[dessalines]

A low-bandwidth mode could also decrease the thumbnail size when requesting from pictrs, that'd be easy enough.