lint(track_config): check hello-world status (#436)

With this commit, `configlet lint` now checks that a track-level
`config.json` file follows the below rule:

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

Co-authored-by: ee7 <45465154+ee7@users.noreply.github.com>

src/lint/track_config.nim

@@ -79,6 +79,15 @@ proc isValidPracticeExercise(data: JsonNode; context: string;
     ]
     result = allTrue(checks)
 
+    const k = "status"
+    if result and data["slug"].getStr() == "hello-world" and data.hasKey(k):
+      let statusVal = data[k].getStr()
+      if statusVal != "active":
+        let msg = &"The hello-world Practice Exercise has a {q k} of {q statusVal}, " &
+                   "but for that exercise, either the value must be `active` or the " &
+                   "key/value pair must be omitted (which implies `active`)"
+        result.setFalseAndPrint(msg, path)
+
 proc hasValidExercises(data: JsonNode; path: Path): bool =
   const k = "exercises"
   if hasObject(data, k, path):