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
if (concreteIndices == null || concreteIndices.length == 0) {
            throw new IllegalArgumentException("Index name is required");
        }
        Metadata metadata = clusterService.state().metadata();
        List<String> writeIndices = new ArrayList<>();
        SortedMap<String, IndexAbstraction> lookup = metadata.getIndicesLookup();
        for (Index index : concreteIndices) {
            IndexAbstraction ia = lookup.get(index.getName());
            if (ia != null && ia.getParentDataStream() != null) {
                Index writeIndex = metadata.index(ia.getParentDataStream().getWriteIndex()).getIndex();
                if (writeIndex.equals(index)) {
                    writeIndices.add(index.getName());
                }
            }
        }
        if (writeIndices.size() > 0) {
            throw new IllegalArgumentException(
                "cannot add a block to the following data stream write indices ["
                    + Strings.collectionToCommaDelimitedString(writeIndices)
                    + "]"
            );
        }
        clusterService.submitStateUpdateTask(
            "add-index-block-[" + request.getBlock().name + "]-" + Arrays.toString(concreteIndices),
            new AddBlocksTask(request, listener),
            ClusterStateTaskConfig.build(Priority.URGENT, request.masterNodeTimeout()),
            addBlocksExecutor
        );
    }
    private class AddBlocksExecutor implements ClusterStateTaskExecutor<AddBlocksTask> {