### Description

It should be enough to have ShardId + nodeId key in `routingToDataPath` to find the necessary data path. 
Changing the key would allow us to minimize the size of ClusterInfo size and find the data path when shard changes its status.

`ClusterInfo` might be sent over the wire when cluster allocation explain is executed with `includeDiskInfo=true`.
ShardRouting -> ShardId + nodeId conversion is trivial. The oposit would require additional information that could be faked.

Current key is also used in here:
https://github.com/elastic/elasticsearch/blob/9ebbe1c62bf0157d332f20f392544a1921a710df/server/src/main/java/org/elasticsearch/cluster/ClusterInfo.java#L149-L154
where it produces a string with ShardRouting#shortSummary that is excessive and might be simplified to ShardId + nodeId as well
server/src/test/java/org/elasticsearch/cluster/DiskUsageTests.java
import org.elasticsearch.index.shard.ShardId;
import org.elasticsearch.index.shard.ShardPath;
import org.elasticsearch.index.store.StoreStats;
import org.elasticsearch.monitor.fs.FsInfo;
import org.elasticsearch.test.ESTestCase;
import java.nio.file.Path;
import java.util.HashMap;
import java.util.Map;
import static java.util.Collections.emptyMap;
import static java.util.Collections.emptySet;
import static org.hamcrest.Matchers.equalTo;
public class DiskUsageTests extends ESTestCase {
    public void testDiskUsageCalc() {
        DiskUsage du = new DiskUsage("node1", "n1", "random", 100, 40);
        assertThat(du.getFreeDiskAsPercentage(), equalTo(40.0));
        assertThat(du.getUsedDiskAsPercentage(), equalTo(100.0 - 40.0));
        assertThat(du.getFreeBytes(), equalTo(40L));
        assertThat(du.getUsedBytes(), equalTo(60L));
        assertThat(du.getTotalBytes(), equalTo(100L));
        DiskUsage du2 = new DiskUsage("node1", "n1", "random", 100, 55);
        assertThat(du2.getFreeDiskAsPercentage(), equalTo(55.0));
        assertThat(du2.getUsedDiskAsPercentage(), equalTo(45.0));
        assertThat(du2.getFreeBytes(), equalTo(55L));
        assertThat(du2.getUsedBytes(), equalTo(45L));
        assertThat(du2.getTotalBytes(), equalTo(100L));
        
        
        DiskUsage du3 = new DiskUsage("node1", "n1", "random", 100, 101);
        assertThat(du3.getFreeDiskAsPercentage(), equalTo(101.0));
        assertThat(du3.getFreeBytes(), equalTo(101L));