Add validation rule

The "exercises.practice[].status" value must, if "exercises.practice[].slug" is equal to hello-world, be either omitted or the string active

Refs: exercism#249

src/lint/track_config.nim

@@ -79,6 +79,12 @@ proc isValidPracticeExercise(data: JsonNode; context: string;
     ]
     result = allTrue(checks)
 
+    if result and data["slug"].getStr() == "hello-world" and data.hasKey("status"):
+      let statusKey = data["status"].getStr()
+      if not (statusKey == "active"):
+        result.setFalseAndPrint(&"The value of {format(context)}.status is `{format(statusKey)}`, but it must be `active` or absent for the hello-world exercise",
+            path)
+
 proc hasValidExercises(data: JsonNode; path: Path): bool =
   const k = "exercises"
   if hasObject(data, k, path):