group dataset files (#118739) (#119045)

*.csv files used for creating data and *.csv-spec used to define test scenarios are blending in the resource directory.
This change moves all *.csv files to data/*.csv so that it is easier to distinguish between data and specs.
This allows to have a quicker overview of existing data when starting a new spec.

Author: idegtiarenko

x-pack/plugin/esql/qa/testFixtures/src/main/java/org/elasticsearch/xpack/esql/CsvTestsDataLoader.java

@@ -362,7 +362,7 @@ private static void load(RestClient client, TestsDataset dataset, Logger logger,
         if (mapping == null) {
             throw new IllegalArgumentException("Cannot find resource " + mappingName);
         }
-        final String dataName = "/" + dataset.dataFileName;
+        final String dataName = "/data/" + dataset.dataFileName;
         URL data = CsvTestsDataLoader.class.getResource(dataName);
         if (data == null) {
             throw new IllegalArgumentException("Cannot find resource " + dataName);