### 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/routing/allocation/decider/DiskThresholdDeciderUnitTests.java
doTestCannotAllocateDueToLackOfDiskResources(false);
    }
    public void testCannotAllocateDueToLackOfDiskResourcesWithMaxHeadroom() {
        doTestCannotAllocateDueToLackOfDiskResources(true);
    }
    private void doTestCanRemainUsesLeastAvailableSpace(boolean testMaxHeadroom) {
        ClusterSettings nss = new ClusterSettings(Settings.EMPTY, ClusterSettings.BUILT_IN_CLUSTER_SETTINGS);
        DiskThresholdDecider decider = new DiskThresholdDecider(Settings.EMPTY, nss);
        Map<ShardRouting, String> shardRoutingMap = new HashMap<>();
        DiscoveryNode node_0 = new DiscoveryNode(
            "node_0",
            buildNewFakeTransportAddress(),
            Collections.emptyMap(),
            new HashSet<>(DiscoveryNodeRole.roles()),
            Version.CURRENT
        );
        DiscoveryNode node_1 = new DiscoveryNode(
            "node_1",
            buildNewFakeTransportAddress(),
            Collections.emptyMap(),
            new HashSet<>(DiscoveryNodeRole.roles()),
            Version.CURRENT
        );
        Metadata metadata = Metadata.builder()
            .put(IndexMetadata.builder("test").settings(settings(Version.CURRENT)).numberOfShards(1).numberOfReplicas(1))
            .build();
        final IndexMetadata indexMetadata = metadata.index("test");
        ShardRouting test_0 = ShardRouting.newUnassigned(
            new ShardId(indexMetadata.getIndex(), 0),
            true,