ES|QL: Move SET command out of snapshot and move validation to single settings (#137204)

Author: luigidellaquila

x-pack/plugin/esql/src/main/antlr/EsqlBaseParser.g4

@@ -24,8 +24,7 @@ import Expression,
        Join;
 
 statements
-    : {this.isDevVersion()}? setCommand+ singleStatement EOF
-    | singleStatement EOF
+    : setCommand* singleStatement EOF
     ;
 
 singleStatement

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

@@ -1285,7 +1285,7 @@ public enum Cap {
         /**
          * Support for the SET command.
          */
-        SET_COMMAND(Build.current().isSnapshot()),
+        SET_COMMAND,
 
         /**
          * (Re)Added EXPLAIN command