mimir-distributed 5.8 release notes (#12250)

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#### What this PR does

This PR adds release notes for the Mimir Helm chart version 5.8 release.

#### Which issue(s) this PR fixes or relates to

Fixes grafana/mimir-squad#3152

#### Checklist

- [ ] Tests updated.
- [X] Documentation added.
- [X] `CHANGELOG.md` updated - the order of entries should be
`[CHANGE]`, `[FEATURE]`, `[ENHANCEMENT]`, `[BUGFIX]`. If changelog entry
is not needed, please add the `changelog-not-needed` label to the PR.
- [ ]
[`about-versioning.md`](https://github.com/grafana/mimir/blob/main/docs/sources/mimir/configure/about-versioning.md)
updated with experimental features.

Author: tacole02

docs/sources/helm-charts/mimir-distributed/release-notes/v5.8.md

@@ -0,0 +1,32 @@
+---
+title: "Grafana Mimir Helm chart version 5.8 release notes"
+menuTitle: "V5.8 release notes"
+description: "Release notes for Grafana Mimir Helm chart version 5.8"
+weight: 300
+---
+
+# Grafana Mimir Helm chart version 5.8 release notes
+
+Grafana Labs is excited to announce version 5.8 of the Grafana Mimir Helm chart, which is compatible with Grafana Mimir v2.17 and Grafana Enterprise Metrics (GEM) v2.17. The `mimir-distributed` Helm chart is the best way to install Mimir on Kubernetes.
+
+The highlights that follow include the top features, enhancements, and bug fixes in this release. For a comprehensive list of changes, see the [Helm chart changelog](https://github.com/grafana/mimir/tree/main/operations/helm/charts/mimir-distributed/CHANGELOG.md).
+
+## Important changes
+
+KEDA autoscaling has changed `kedaAutoscaling.toPromQLLabelSelector` from an object to a list of strings, adding support for all PromQL operators.
+
+The Memcached timeout for the ruler-storage cache has increased from 200 milliseconds to 500 milliseconds.
+
+Grafana Mimir now exports OTel traces instead of Jaeger traces. As a result, the environment variable `JAEGER_REPORTER_MAX_QUEUE_SIZE` is no longer set by default. Components use OTel's default value of 2048 unless explicitly configured. You can still configure `JAEGER_REPORTER_MAX_QUEUE_SIZE` if you configure tracing using Jaeger environment variables, and you can always set `OTEL_BSP_MAX_QUEUE_SIZE` for OTel configuration. For more information, refer to [Configure Grafana Mimir tracing](https://grafana.com/docs/mimir/<MIMIR_VERSION>/configure/configure-tracing/) in the Mimir documentation.
+
+The rollout-operator has been updated to the latest release, which includes support for OTEL\_ tracing environment variables.
+
+Memberlist configuration for ingesters now enables `memberlist.abort-if-fast-join-fails`.
+
+Memcached now sets resource requests for the Memcached Prometheus exporter by default.
+
+A new `store_gateway.grpcMaxQueryResponseSizeBytes` value has been added to set the maximum store-gateway gRPC query response send size, and corresponding querier receive size, with a default of 200MB.
+
+## Features and enhancements
+
+There are new values for setting annotations and labels for the rollout-operator.