Update CHANGELOG to document new distributor.Push() errors (#6406)

* Update CHANGELOG to document new distributor.Push() errors

Signed-off-by: Yuri Nikolic <durica.nikolic@grafana.com>

* Adding the PR number

Signed-off-by: Yuri Nikolic <durica.nikolic@grafana.com>

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Signed-off-by: Yuri Nikolic <durica.nikolic@grafana.com>

CHANGELOG.md

@@ -12,6 +12,11 @@
 * [CHANGE] Ingester: changed the default value for the experimental configuration parameter `-blocks-storage.tsdb.early-head-compaction-min-estimated-series-reduction-percentage` from 10 to 15. #6186
 * [CHANGE] Ingester: `/ingester/push` HTTP endpoint has been removed. This endpoint was added for testing and troubleshooting, but was never documented or used for anything. #6299
 * [CHANGE] Experimental setting `-log.rate-limit-logs-per-second-burst` renamed to `-log.rate-limit-logs-burst-size`. #6230
+* [CHANGE] Distributor: instead of errors with HTTP status codes, `Push()` now returns errors with gRPC codes: #6377
+* * `replicasDidNotMatchError` is mapped to `codes.AlreadyExists` instead of `http.StatusAccepted` (202).
+* * `tooManyClustersError` and `validationError` are mapped to `codes.FailedPrecondition` instead of `http.BadRequest` (400).
+* * `ingestionRateLimitedError` is mapped to `codes.ResourceExhausted` instead of `http.StatusTooManyRequests` (429).
+* * `requestRateLimitedError` is mapped to `codes.Unavailable` or `codes.ResourceExhausted` instead of the non-standard `529` (The service is overloaded) or `http.StatusTooManyRequests` (429).
 * [FEATURE] Query-frontend: add experimental support for query blocking. Queries are blocked on a per-tenant basis and is configured via the limit `blocked_queries`. #5609
 * [FEATURE] Vault: Added support for new Vault authentication methods: `AppRole`, `Kubernetes`, `UserPass` and `Token`. #6143
 * [ENHANCEMENT] Ingester: exported summary `cortex_ingester_inflight_push_requests_summary` tracking total number of inflight requests in percentile buckets. #5845