ESQL: Make _tsid presentable

- Add an ability to present the TSID_DATA_TYPE as KEYWORD.
- Add tests for the TopN optimization with METADATA _tsid

Author: leontyevdv

x-pack/plugin/esql/qa/testFixtures/src/main/resources/topN.csv-spec

@@ -168,3 +168,21 @@ FROM employees
 avg_worked_seconds:long | birth_date:date      | emp_no:i | gender:k | height:d | height.float:d     | height.half_float:d | height.scaled_float:d | hire_date:date       | is_rehired:bool      | job_positions:k     | languages:i | languages.byte:i | languages.long:l | languages.short:short | salary:i | salary_change:d | salary_change.int:i | salary_change.keyword:k | salary_change.long:l | still_hired:bool | name:k  | first_name:k | last_name:k
 349086555               | 1961-09-01T00:00:00Z | 10056    | F        | 1.57     | 1.5700000524520874 | 1.5703125           | 1.57                  | 1990-02-01T00:00:00Z | [false, false, true] | [Senior Team Lead]  | 2           | 2                | 2                | 2                     | 33370    | [-5.17, 10.99]  | [-5, 10]            | [-5.17, 10.99]          | [-5, 10]             | true             | Brendon | Bernini      | Brendon
 ;
+
+sortingByTsidMetadataField
+required_capability: ts_command_v0
+required_capability: metadata_tsid_field
+
+TS k8s METADATA _tsid
+| SORT events_received ASC
+| LIMIT 5
+| KEEP events_received, @timestamp, cluster, pod
+;
+
+events_received:long | @timestamp:datetime | cluster:keyword | pod:keyword
+1                    | 2024-05-10T00:00:00.000Z | qa              | one
+1                    | 2024-05-10T00:00:00.000Z | qa              | two
+1                    | 2024-05-10T00:00:00.000Z | qa              | three
+1                    | 2024-05-10T00:00:00.000Z | prod            | one
+1                    | 2024-05-10T00:00:00.000Z | prod            | two
+;

x-pack/plugin/esql/src/main/java/org/elasticsearch/xpack/esql/action/PositionToXContent.java

@@ -28,6 +28,7 @@
 import org.elasticsearch.xcontent.XContentParser;
 import org.elasticsearch.xcontent.XContentParserConfiguration;
 import org.elasticsearch.xcontent.XContentType;
+import org.elasticsearch.xpack.esql.core.expression.MetadataAttribute;
 
 import java.io.IOException;
 
@@ -108,6 +109,10 @@ protected XContentBuilder valueToXContent(XContentBuilder builder, ToXContent.Pa
                         // https://github.com/FasterXML/jackson-dataformats-binary/issues/366
                         val = BytesRef.deepCopyOf(scratch);
                     }
+
+                    if (columnInfo.name().equalsIgnoreCase(MetadataAttribute.TSID_FIELD)) {
+                        return builder.value(TimeSeriesIdFieldMapper.encodeTsid(val));
+                    }
                     return builder.utf8Value(val.bytes, val.offset, val.length);
                 }
             };

x-pack/plugin/esql/src/test/java/org/elasticsearch/xpack/esql/action/EsqlQueryResponseTests.java

@@ -49,6 +49,7 @@
 import org.elasticsearch.geometry.utils.Geohash;
 import org.elasticsearch.h3.H3;
 import org.elasticsearch.index.mapper.BlockLoader;
+import org.elasticsearch.index.mapper.TimeSeriesIdFieldMapper;
 import org.elasticsearch.rest.action.RestActions;
 import org.elasticsearch.search.aggregations.bucket.geogrid.GeoTileUtils;
 import org.elasticsearch.test.AbstractChunkedSerializingTestCase;
@@ -64,6 +65,7 @@
 import org.elasticsearch.xcontent.XContentType;
 import org.elasticsearch.xcontent.json.JsonXContent;
 import org.elasticsearch.xpack.esql.EsqlTestUtils;
+import org.elasticsearch.xpack.esql.core.expression.MetadataAttribute;
 import org.elasticsearch.xpack.esql.core.type.DataType;
 import org.elasticsearch.xpack.esql.planner.PlannerUtils;
 import org.elasticsearch.xpack.esql.type.UnsupportedEsFieldTests;
@@ -1086,6 +1088,36 @@ public void testProfileXContent() {
         }
     }
 
+    public void testKeywordTsidFieldEncoding() {
+        BytesRef tsidValue = (BytesRef) EsqlTestUtils.randomLiteral(DataType.TSID_DATA_TYPE).value();
+        Object expectedEncoded = TimeSeriesIdFieldMapper.encodeTsid(tsidValue);
+
+        for (String columnName : List.of(
+            MetadataAttribute.TSID_FIELD.toLowerCase(Locale.ROOT),
+            MetadataAttribute.TSID_FIELD.toUpperCase(Locale.ROOT)
+        )) {
+            for (String dataType : List.of(DataType.KEYWORD.esType(), DataType.TEXT.esType())) {
+                try (
+                    BytesRefBlock.Builder refBlockBuilder = blockFactory.newBytesRefBlockBuilder(1);
+
+                    EsqlQueryResponse response = new EsqlQueryResponse(
+                        List.of(new ColumnInfoImpl(columnName, dataType, null)),
+                        List.of(new Page(refBlockBuilder.appendBytesRef(tsidValue).build())),
+                        1,
+                        1,
+                        null,
+                        false,
+                        false,
+                        null
+                    )
+                ) {
+                    String json = Strings.toString(wrapAsToXContent(response), true, false);
+                    assertThat(json, org.hamcrest.Matchers.containsString("\"" + expectedEncoded + "\""));
+                }
+            }
+        }
+    }
+
     @Override
     protected void dispose(EsqlQueryResponse esqlQueryResponse) {
         esqlQueryResponse.close();