Update ContentDisposition to refer to RFC 6266 #24231
Description
ContentDisposition was originally created in reference to RFC 2183 which is a non-HTTP spec. This was what the old HTTP spec RFC 2616 refers to (via RFC 1806, later updated by 2183).
RFC 6266 is the current HTTP spec that defines the use of Content-Disposition in HTTP and supersedes the same from RFC 2616.
Appendix B of RFC 6266 lists several fields from RFC 2183 that are omitted including "creation-date", "modification-date", "read-date", and "size". We can deprecate those in ContentDisposition to be removed eventually.