introduce capability

Author: idegtiarenko

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

@@ -1,11 +1,15 @@
 md5
+required_capability: kql_function
+
 ROW value = "test" | EVAL hash = hash("md5", value);
 
 value:keyword | hash:keyword
 test          | 098f6bcd4621d373cade4e832627b4f6
 ;
 
 sha256
+required_capability: kql_function
+
 ROW value = "test" | EVAL hash = hash("sha256", value);
 
 value:keyword | hash:keyword

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

@@ -424,6 +424,11 @@ public enum Cap {
          */
         KQL_FUNCTION(Build.current().isSnapshot()),
 
+        /**
+         * Hash function
+         */
+        HASH_FUNCTION(Build.current().isSnapshot()),
+
         /**
          * Don't optimize CASE IS NOT NULL function by not requiring the fields to be not null as well.
          * https://github.com/elastic/elasticsearch/issues/112704