[AB-xxx] adding/updating documentation for core and experience module

updating asciidoctor plugin version
adding check to not allow duplicate level action configurations
limiting experience level up notification toggle command to be only available if the feature mode is enabled

abstracto-application/abstracto-modules/experience-tracking/experience-tracking-int/src/main/java/dev/sheldan/abstracto/experience/exception/LevelActionAlreadyExistsException.java

@@ -0,0 +1,21 @@
+package dev.sheldan.abstracto.experience.exception;
+
+import dev.sheldan.abstracto.core.exception.AbstractoRunTimeException;
+import dev.sheldan.abstracto.core.templating.Templatable;
+
+public class LevelActionAlreadyExistsException extends AbstractoRunTimeException implements Templatable {
+
+    public LevelActionAlreadyExistsException() {
+        super("Level action already exists.");
+    }
+
+    @Override
+    public String getTemplateName() {
+        return "level_action_already_exists_exception";
+    }
+
+    @Override
+    public Object getTemplateModel() {
+        return new Object();
+    }
+}