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
final Metadata.Builder metadata = Metadata.builder(currentState.metadata());
        final Set<Index> indicesToAddBlock = new HashSet<>();
        for (Index index : indices) {
            metadata.getSafe(index); 
            if (currentState.blocks().hasIndexBlock(index.getName(), block.block)) {
                logger.debug("index {} already has block {}, ignoring", index, block.block);
            } else {
                indicesToAddBlock.add(index);
            }
        }
        if (indicesToAddBlock.isEmpty()) {
            return Tuple.tuple(currentState, Map.of());
        }
        final ClusterBlocks.Builder blocks = ClusterBlocks.builder(currentState.blocks());
        final Map<Index, ClusterBlock> blockedIndices = new HashMap<>();
        for (Index index : indicesToAddBlock) {
            ClusterBlock indexBlock = null;
            final Set<ClusterBlock> clusterBlocks = currentState.blocks().indices().get(index.getName());
            if (clusterBlocks != null) {
                for (ClusterBlock clusterBlock : clusterBlocks) {
                    if (clusterBlock.id() == block.block.id()) {
                        
                        indexBlock = clusterBlock;
                        break;
                    }
                }
            }
            if (indexBlock == null) {
                
                indexBlock = createUUIDBasedBlock(block.block);