Document to provide PLUS group with information about desirable diagnostics in QUIC and PLUS headers.

To render the XML file, use XML2RFC tool: https://xml2rfc.tools.ietf.org/

The XML2RFC file format is described in https://tools.ietf.org/html/rfc7991

The most current version is available at: https://tools.ietf.org/html/draft-dolson-transport-middlebox-01 or the datatracker: https://datatracker.ietf.org/doc/draft-dolson-transport-middlebox/