Add stats scores test

Author: carlosdelest

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

@@ -521,7 +521,6 @@ book_no:keyword |  _score:double
 8678            | 0.0
 ;
 
-
 disjunctionScoresMultipleClauses
 
 required_capability: metadata_score
@@ -544,3 +543,17 @@ book_no:keyword |  _score:double
 4023            | 1.5062403678894043
 2924            | 1.2732219696044922
 ;
+
+statsScores
+
+required_capability: metadata_score
+required_capability: match_function
+required_capability: full_text_functions_in_stats_where
+
+from books metadata _score 
+| stats avg_score = avg(_score) where match(title, "Lord Rings", {"operator": "AND"})
+;
+
+avg_score:double
+3.869828939437866 
+;