datajson: output context to "context"

Using `alert.extra` was not really reflecting the nature of what
was added. So renaming it to `alert.context`.

etc/schema.json

@@ -19,10 +19,10 @@
                 "gid": {
                     "type": "integer"
                 },
-                "extra": {
+                "context": {
                     "type": "object",
                     "additionalProperties": true,
-                    "description": "Extra data created by keywords such as dataset with JSON"
+                    "description": "Extra context data created by keywords such as dataset with JSON"
                 },
                 "metadata": {
                     "type": "object",
@@ -2999,8 +2999,8 @@
                             }
                         },
                         "additionalProperties": true
-                    },
+                    }
-                },
+                }
             },
             "optional": true
         },

src/output-json-alert.c

@@ -254,7 +254,7 @@ void AlertJsonHeader(const Packet *p, const PacketAlert *pa, SCJsonBuilder *js,
     }
 
     if (pa->json_info.json_string != NULL) {
-        SCJbOpenObject(js, "extra");
+        SCJbOpenObject(js, "context");
         const struct ExtraDataJsonList *json_info = &pa->json_info;
         while (json_info) {
             SCJbSetFormatted(js, json_info->json_string);