Tiny supportability nit: today we emit these log messages when adding a write block to an index:

```
[2022-03-22T19:43:26,897][INFO ][o.e.c.m.MetadataIndexStateService] [node_t1] adding block write to indices [[test-blocks/eLkrYpm_S3WNemfWpXrhPA]]
[2022-03-22T19:43:26,933][INFO ][o.e.c.m.MetadataIndexStateService] [node_t1] completed adding block write to indices [test-blocks]
```

This is kind of confusing, a `block write` sounds like we're writing a block of data. It's not clear that `write` is variable (we also say `block read`) or the name of a block setting. I think we should word this as `adding [index.blocks.write] block to indices` instead.
server/src/main/java/org/elasticsearch/cluster/metadata/MetadataIndexStateService.java
public void onFailure(Exception e) {
            listener.onFailure(e);
        }
        @Override
        public boolean mustAck(DiscoveryNode discoveryNode) {
            return true;
        }
        @Override
        public void onAllNodesAcked() {
            listener.onResponse(AcknowledgedResponse.of(true));
        }
        @Override
        public void onAckFailure(Exception e) {
            listener.onResponse(AcknowledgedResponse.of(false));
        }
        @Override
        public void onAckTimeout() {
            listener.onResponse(AcknowledgedResponse.FALSE);
        }
        @Override
        public TimeValue ackTimeout() {
            return request.ackTimeout();
        }
        @Override
        public void clusterStateProcessed(ClusterState oldState, ClusterState newState) {
            assert false : "not called";
        }
    }
}