RateLimit headers: Azure and Kong implementation landed. Request for feedback on Intermediaries and Cache

Dear all,

me, Alex and the community are continuing
our work on ratelimit headers.

Here you can find the updates, your feedback
is precious to move on with the spec :)

## Implementors
Following the advices coming from IETF-106
we got more support from API Gateway implementors:

- Azure API Gateway added some features to
  expose ratelimit counters, so you can use them
  to implement this specification [1]
- Kong 2.0.0 implemented the specification and
  supports now providing the mandatory part
  of the headers [2]
- Express-Gateway, a nodejs gateway with more than 2k stars on github
  is working on that. You can test it using this docker image [3]

## Intermediaries and Caching
We have a PR [4] on Intermediaries and Caching,
and got some useful feedback from Martin and Erik (thanks!).
Further feedbacks are really appreciated, especially on Caching!

## Scope
After Roy's comment, I made a proposal for addressing
the scope issue in a way that is consistent with Retry-After [5].
If that won't work, we could address that only in ratelimit spec
passing the scope as an header parameter [6].

Thanks for all your guidance
and support,
R.





[1]:
https://azure.microsoft.com/en-ca/updates/azure-api-management-update-january-2020/
[2]: https://github.com/Kong/kong/pull/5335
[3]: https://github.com/ioggstream/docker-express-gateway-ratelimit
[4]: https://github.com/ioggstream/draft-polli-ratelimit-headers/pull/76
[5]: https://github.com/httpwg/http-core/pull/317#issuecomment-585634120
[6]:
https://github.com/ioggstream/draft-polli-ratelimit-headers/pull/79/files