Add `infinite_scroll_enabled` to user settings.

### Pre-Flight checklist - [x] Did you check to see if this issue already exists? - [x] This is a single feature request. (Do not put multiple feature requests in one issue) - [x] This is not a question or discussion. (Use https://lemmy.ml/c/jerboa for that) ### Describe The Feature Request Below Add `infinite_scroll_enabled` to user settings.