stats: add rules skipped

Rule skipped is a count of the number of rules that are skipped due to
missing requirements.

Feature: #6637
(cherry picked from commit b453eea150)

etc/schema.json

@@ -4851,6 +4851,9 @@
                                     },
                                     "rules_failed": {
                                         "type": "integer"
+                                    },
+                                    "rules_skipped": {
+                                        "type": "integer"
                                     }
                                 },
                                 "additionalProperties": false

src/output-json-stats.c

@@ -98,6 +98,7 @@ static json_t *EngineStats2Json(const DetectEngineCtx *de_ctx,
                             json_integer(sig_stat->good_sigs_total));
         json_object_set_new(jdata, "rules_failed",
                             json_integer(sig_stat->bad_sigs_total));
+        json_object_set_new(jdata, "rules_skipped", json_integer(sig_stat->skipped_sigs_total));
     }
 
     return jdata;