Make thread pool configurable

src/main/java/com/btk5h/skriptdb/skript/EffExecuteStatement.java

@@ -51,7 +51,7 @@ public class EffExecuteStatement extends Delay {
   static String lastError;
 
   private static final ExecutorService threadPool =
-      Executors.newFixedThreadPool(Runtime.getRuntime().availableProcessors());
+      Executors.newFixedThreadPool(SkriptDB.getInstance().getConfig().getInt("thread-pool-size"));
 
   private Expression<String> query;
   private Expression<HikariDataSource> dataSource;