upd: add option for reply depth

Created by: dakkar

@ShittyKopper wrote this, and suggested that someone else made a PR. So here it is.

This allows changing how many replies to fetch when showing a thread, before showing the "View thread continuation »" link.

Checklist

• Read the contribution guide
• Test working in a local environment
• (If needed) Add story of storybook
• (If needed) Update CHANGELOG.md
• (If possible) Add tests