Update design of lists in content

[gnprice]

The alignment and spacing of lists (<ul> and <ol> elements) is getting an update. We should apply that update.

References

• Sibling issue: Update design of blockquotes in content #1493
• Web PR: markdown: Adjust list, blockquote styles to spec. zulip#34529
• Web issue (covering many other things too): UI redesign: message typography, including mention pills zulip#22022
• Design thread: #design > updating lists, blockquotes to spec