[Regression] GitLab no longer sends 429 Retry-After header on self-managed since 13.0

Previously Gitlab (self-managed) included the Retry-After header on 429 Too many requests, when rate-limiting was setup in the Admin settings.

Seems like starting with version around 13.0, this stopped being the case.

GitLab.com at least includes these headers:

{
  "ratelimit-limit": "600",
  "ratelimit-observed": "64",
  "ratelimit-remaining": "536",
  "ratelimit-reset": "1594731604",
  "ratelimit-resettime": "Tue, 14 Jul 2020 13:00:04 GMT"
}

Gitlab self-managed no longer includes any headers.

What's the plan here? Do you see yourself supporting these headers in the future or not?

Libraries like python-gitlab, have special code to handle 429 errors with this header:

https://github.com/python-gitlab/python-gitlab/blob/master/gitlab/init.py#L550

Related to #199738, but different

TODO

• fix bug
• add details about Retry-After header to https://docs.gitlab.com/ee/api/#status-codes & https://docs.gitlab.com/ee/security/rate_limits.html