ESQL: TOP support for strings (elastic#113183) (elastic#113408)

Adds support to the `TOP` aggregation for `keyword` and `text` field
types.

Closes elastic#109849

Author: nik9000

docs/changelog/113183.yaml

@@ -0,0 +1,6 @@
+pr: 113183
+summary: "ESQL: TOP support for strings"
+area: ES|QL
+type: feature
+issues:
+ - 109849

docs/reference/esql/functions/kibana/definition/top.json

@@ -635,6 +635,11 @@ tasks.named('stringTemplates').configure {
     it.inputFile = topAggregatorInputFile
     it.outputFile = "org/elasticsearch/compute/aggregation/TopBooleanAggregator.java"
   }
+  template {
+    it.properties = bytesRefProperties
+    it.inputFile = topAggregatorInputFile
+    it.outputFile = "org/elasticsearch/compute/aggregation/TopBytesRefAggregator.java"
+  }
   template {
     it.properties = ipProperties
     it.inputFile = topAggregatorInputFile