chore: rename tool span tag to tool_name

Author: manuel-alvarez-alvarez

dd-java-agent/agent-aiguard/src/main/java/com/datadog/aiguard/AIGuardInternal.java

@@ -63,7 +63,7 @@ public BadConfigurationException(final String message) {
 
   static final String SPAN_NAME = "ai_guard";
   static final String TARGET_TAG = "ai_guard.target";
-  static final String TOOL_TAG = "ai_guard.tool";
+  static final String TOOL_TAG = "ai_guard.tool_name";
   static final String ACTION_TAG = "ai_guard.action";
   static final String REASON_TAG = "ai_guard.reason";
   static final String BLOCKED_TAG = "ai_guard.blocked";