### 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
assertThat(
            new DiskThresholdDecider.DiskUsageWithRelocations(new DiskUsage("n", "n", "/dev/null", 1000L, 1000L), 0)
                .getFreeDiskAsPercentage(),
            equalTo(100.0)
        );
        assertThat(
            new DiskThresholdDecider.DiskUsageWithRelocations(new DiskUsage("n", "n", "/dev/null", 1000L, 500L), 0)
                .getFreeDiskAsPercentage(),
            equalTo(50.0)
        );
        assertThat(
            new DiskThresholdDecider.DiskUsageWithRelocations(new DiskUsage("n", "n", "/dev/null", 1000L, 500L), 100)
                .getFreeDiskAsPercentage(),
            equalTo(40.0)
        );
        assertThat(
            new DiskThresholdDecider.DiskUsageWithRelocations(new DiskUsage("n", "n", "/dev/null", 1000L, 1000L), 0)
                .getUsedDiskAsPercentage(),
            equalTo(0.0)
        );
        assertThat(
            new DiskThresholdDecider.DiskUsageWithRelocations(new DiskUsage("n", "n", "/dev/null", 1000L, 500L), 0)
                .getUsedDiskAsPercentage(),
            equalTo(50.0)
        );
        assertThat(
            new DiskThresholdDecider.DiskUsageWithRelocations(new DiskUsage("n", "n", "/dev/null", 1000L, 500L), 100)
                .getUsedDiskAsPercentage(),
            equalTo(60.0)
        );