Docs: Move and update FAQ (Diátaxis) (#9908)

* Move FAQ to How-to navigation area, pending updates

* Remove duplicate /faq in TOC, experiment with :titlesonly: in the how-to TOC

* Rework first batch of FAQ entries to be Questions with Answers and cross-references

* Restore entry in Troubleshooting

* Less frisky question

* Re-order FAQ into top-levels

* Adds a seealso, change some literals to code-blocks

* Clarify a few random items

* Re-add :hidden: for TOC - not sure it makes any difference

Author: benjaoming