SQL: Translate MIN/MAX on keyword fields as FIRST/LAST

Although the translation rule was implemented in the `Optimizer`,
the rule was not added in the list of rules to be executed.

Relates to elastic#41195
Follows elastic#37936

Author: matriv

x-pack/plugin/sql/qa/src/main/resources/agg.csv-spec

@@ -414,6 +414,17 @@ SELECT COUNT(ALL last_name)=COUNT(ALL first_name) AS areEqual, COUNT(ALL first_n
 false          |90             |100
 ;
 
+topHitsAsMinAndMax
+schema::gender:s|first:s|last:s
+SELECT gender, MIN(first_name) as first, MAX(first_name) as last FROM test_emp GROUP BY gender ORDER BY gender;
+
+    gender     |   first       |   last
+---------------+---------------+---------------
+null           |   Berni       |   Patricio
+F              |   Alejandro   |   Xinglin
+M              |   Amabile     |   Zvonko
+;
+
 topHitsWithOneArgAndGroupBy
 schema::gender:s|first:s|last:s
 SELECT gender, FIRST(first_name) as first, LAST(first_name) as last FROM test_emp GROUP BY gender ORDER BY gender;

x-pack/plugin/sql/src/main/java/org/elasticsearch/xpack/sql/optimizer/Optimizer.java

@@ -149,6 +149,7 @@ protected Iterable<RuleExecutor<LogicalPlan>.Batch> batches() {
 
         Batch aggregate = new Batch("Aggregation Rewrite",
                 //new ReplaceDuplicateAggsWithReferences(),
+                new ReplaceMinMaxWithTopHits(),
                 new ReplaceAggsWithMatrixStats(),
                 new ReplaceAggsWithExtendedStats(),
                 new ReplaceAggsWithStats(),