Add SIEM package category (#5128)

Removed changes from:
- detection_rules/etc/packages.yaml

(selectively cherry picked from commit e147188)

Author: shashank-elastic

detection_rules/etc/packages.yaml

@@ -11,6 +11,8 @@ package:
       elastic:
         capabilities:
         - security
+        # Added siem category as these rules are used by the Elastic Security detection engine for security monitoring
+        - siem
         subscription: basic
       kibana.version: ^9.1.0
     description: Prebuilt detection rules for Elastic Security