note on deprecating redis

Signed-off-by: Vladimir Varankin <[email protected]>

docs/sources/mimir/release-notes/v2.14.md

@@ -46,6 +46,9 @@ The following featues of store-gateway are changed: `-blocks-storage.bucket-stor
 `-blocks-storage.bucket-store.index-header.lazy-loading-concurrency-queue-timeout` is set to five seconds;
 `-blocks-storage.bucket-store.max-concurrent` is set to 200;
 
+The experimental support for Redis-based caching is now deprecated. It will be removed in the future major release. Users are encouraged
+to switch to use Memcached.
+
 The following deprecated configuration options were removed in this release:
 
 - The `-ingester.return-only-grpc-errors` option in the ingester