Display Persian (`fa`) pages in right-to-left (RTL) fashion & other improvements

[chalin]

• [x] google/docsy-example#294
• [x] google/docsy-example#300
• [x] google/docsy-example#302
• [x] #304
• [x] #305 - brings in RTL support for projects using Docsy via Hugo modules
• [x] #322
• [x] #325
• [x] google/docsy#2019
• [ ] Upgrade Docsy

[theletterf]

It'd be nice to see an example of a full sidebar, with a ToC and other elements, like here: https://www.docsy.dev/docs