fix(textlintrc): add allowlist filter for custom markdown syntax

Author: fassko

.textlintrc.json

@@ -2,6 +2,11 @@
   "plugins": {
     "mdx": true
   },
+  "filters": {
+    "allowlist": {
+      "allow": ["/^:::[a-zA-Z]+\\[[^\\]]*\\][\\s\\S]*?^:::\\s*$/gm"]
+    }
+  },
   "rules": {
     "one-sentence-per-line": true
   }