Proposal for updated SF format for No-Vary-Search params

Hi HTTP Working Group,

As a result of some feedback from Working Group Last Call for the
No-Vary-Search document (
https://datatracker.ietf.org/doc/draft-ietf-httpbis-no-vary-search/), we
have a new proposal to update the structured field format for the `params`
field in the No-Vary-Search header.

The proposal is essentially to update the `params` field to be an inner
list of strings, and only allow for it to be present when `except` is not
present. This allows us to simplify the algorithm, but based on
https://chromestatus.com/metrics/feature/timeline/popularity/4425, potentially
breaks interoperability for those that have already deployed the current
draft's syntax in production. From the perspective of one implementation,
if we were to merge this change, Chrome's plan is to support both syntaxes
for a short time before deprecating the older syntax.

Please take a look at https://github.com/httpwg/http-extensions/pull/3374
for the full proposed change, and we would appreciate it if you could
respond with any comments or concerns.

Thank you!

Best,
Nidhi obo the authors