Promote experimental features (#4003)

* Distributor request limits are stable
* Exemplar API and corresponding flags are stable

See #3979

Signed-off-by: Nick Pillitteri <nick.pillitteri@grafana.com>

docs/sources/mimir/operators-guide/configure/about-versioning.md

@@ -53,14 +53,7 @@ The following features are currently experimental:
     - `-ruler.alerting-rules-evaluation-enabled`
 - Distributor
   - Metrics relabeling
-  - Request rate limit
-    - `-distributor.request-rate-limit`
-    - `-distributor.request-burst-limit`
   - OTLP ingestion path
-- Exemplar storage
-  - `-ingester.max-global-exemplars-per-user`
-  - `-ingester.exemplars-update-period`
-  - API endpoint `/api/v1/query_exemplars`
 - Hash ring
   - Disabling ring heartbeat timeouts
     - `-distributor.ring.heartbeat-timeout=0`