PEP 691: Refactor based on Feedback (#2592)

* Describe JSON format first and more clearly
* Clarify versioning
* Move content types down and flesh them out more
* Expand the conneg section
* Expand upon the impact to PEP 458
* Add alternative mechanisms for conneg
* Provide recommendations to clients and servers
* Add a FAQ for implications for static file serving
* Add a FAQ to clarify that TUF targets != URLs
* Add a FAQ for application/json
* Add a FAQ about PyPI
* Add support for PEP 629 in the JSON response body
* Add PyPI to the appendix
* Recommend ;q=0 on text/html
* Rename the dist-info-metadata-available field
* Update the PEP-Delegate to Brett Cannon