Today submitting an unbatched `ClusterStateUpdateTask` to the `MasterService` is deprecated, and devs are encouraged to write their own batching executor instead. In principle this makes it possible to combine updates without incurring the costs of building a whole new `ClusterState` on each iteration, but in practice most implementations don't work at a lower level and just iteratively update a `ClusterState`. Moreover creating new `ClusterState` instances is nothing like as expensive as once it was.

We should accept this and provide some friendlier utilities for writing batched cluster state updates, ideally leaving the developer to express the desired per-task update as a `ClusterState -> ClusterState` operator.
server/src/main/java/org/elasticsearch/health/metadata/HealthMetadataService.java
HealthMetadata.Disk.Builder builder = HealthMetadata.Disk.newBuilder(initialHealthMetadata.getDiskMetadata());
            if (CLUSTER_ROUTING_ALLOCATION_HIGH_DISK_WATERMARK_SETTING.getKey().equals(setting)) {
                builder.highWatermark(value, setting);
            }
            if (CLUSTER_ROUTING_ALLOCATION_DISK_FLOOD_STAGE_WATERMARK_SETTING.getKey().equals(setting)) {
                builder.floodStageWatermark(value, setting);
            }
            if (CLUSTER_ROUTING_ALLOCATION_DISK_FLOOD_STAGE_FROZEN_WATERMARK_SETTING.getKey().equals(setting)) {
                builder.frozenFloodStageWatermark(value, setting);
            }
            if (CLUSTER_ROUTING_ALLOCATION_DISK_FLOOD_STAGE_FROZEN_MAX_HEADROOM_SETTING.getKey().equals(setting)) {
                builder.frozenFloodStageMaxHeadroom(value, setting);
            }
            if (CLUSTER_ROUTING_ALLOCATION_HIGH_DISK_MAX_HEADROOM_SETTING.getKey().equals(setting)) {
                builder.highMaxHeadroom(value, setting);
            }
            if (CLUSTER_ROUTING_ALLOCATION_DISK_FLOOD_STAGE_MAX_HEADROOM_SETTING.getKey().equals(setting)) {
                builder.floodStageMaxHeadroom(value, setting);
            }
            final var finalHealthMetadata = new HealthMetadata(builder.build());
            return finalHealthMetadata.equals(initialHealthMetadata)
                ? clusterState
                : clusterState.copyAndUpdate(b -> b.putCustom(HealthMetadata.TYPE, finalHealthMetadata));
        }
    }
    /**
     * A health metadata cluster state update task that reads the settings from the local node and resets the
     * health metadata in the cluster state with these values.
     */
    static class InsertHealthMetadata extends UpsertHealthMetadataTask {