Update Registry documentation according to SE-0292 amendment (#3624)

* Add example of redirecting to CDN
* Update example problem description
* Amend rules for package names
* Link headers for version-specific manifests should include swift-tools-version attribute
* Update regular expression pattern for version-specific manifest filenames
* Add --prefix argument to archive-source command
* Restructure response to GET /{scope}/{name}/{version}
* A release must not have duplicate resources for a given (name, type)
* Add missing .zip extension to URI path expression
* Update regular expression pattern for name in OpenAPI spec

Author: mattt