Add placeholder blurb to Concept Exercise .meta/config.json files

Each Concept Exercise will have to define a blurb, which is a short description of the exercise.
The blurb will be displayed on a track's exercises page (e.g. https://exercism.lol/tracks/csharp/exercises).

This commit adds a placeholder blurb to the .meta/config.json file of each Concept Exercise.

See [the spec](https://github.com/exercism/docs/blob/main/anatomy/tracks/concept-exercises.md#file-metaconfigjson) for more information.

Author: ErikSchierboom

exercises/concept/lucians-luscious-lasagna/.meta/config.json

@@ -1,4 +1,5 @@
 {
+  "blurb": "TODO: add blurb for lucians-luscious-lasagna exercise",
   "authors": [
     {
       "github_username": "mpizenberg",
@@ -9,10 +10,18 @@
       "exercism_username": "ceddlyburge"
     }
   ],
-  "forked_from": ["fsharp/lucians-luscious-lasagna"],
+  "forked_from": [
+    "fsharp/lucians-luscious-lasagna"
+  ],
   "files": {
-    "solution": ["src/LuciansLusciousLasagna.elm"],
-    "test": ["tests/Tests.elm"],
-    "exemplar": [".meta/Exemplar.elm"]
+    "solution": [
+      "src/LuciansLusciousLasagna.elm"
+    ],
+    "test": [
+      "tests/Tests.elm"
+    ],
+    "exemplar": [
+      ".meta/Exemplar.elm"
+    ]
   }
 }