Provide a directory listing for Request, assuming it is an
index for the physical directrory Dir. If the request-path does not end
with /, first return a moved (301 Moved Permanently) reply.
The calling conventions allows for direct calling from
http_handler/3.
History
Extended in 8.1.16 (👉f63ef81) http_reply_dirindex/3 and directory_index/2: option name(Callable) to hook the name cell creation.