Add CHANGELOG.md entry

Signed-off-by: Dimitar Dimitrov <dimitar.dimitrov@grafana.com>

CHANGELOG.md

@@ -11,6 +11,7 @@
   * Query results caching should be more stable as all equivalent queries receive the same cache key, but there may be cache churn on first deploy with the updated format
   * Query blocking can no longer be circumvented with an equivalent query in a different format; see [Configure queries to block](https://grafana.com/docs/mimir/latest/configure/configure-blocked-queries/)
 * [CHANGE] Query-frontend: stop using `-validation.create-grace-period` to clamp how far into the future a query can span.
+* [CHANGE] Anonymous usage statistics tracking: report active series in addition to in-memory series. #8279
 * [FEATURE] Continuous-test: now runable as a module with `mimir -target=continuous-test`. #7747
 * [FEATURE] Store-gateway: Allow specific tenants to be enabled or disabled via `-store-gateway.enabled-tenants` or `-store-gateway.disabled-tenants` CLI flags or their corresponding YAML settings. #7653
 * [FEATURE] New `-<prefix>.s3.bucket-lookup-type` flag configures lookup style type, used to access bucket in s3 compatible providers. #7684