The JSON spec parser should support the new format

[delvedor]

While working on #46522, @polyfractal has discovered that the parsing for _common.json assumes there is only one object to parse, while the new spec format there are two objects.

The parser needs to be updated to adopt the new structure of the JSON spec.
Following, the difference between the old format and the new one.

-  "description": "Parameters that are accepted by all API endpoints.",
-  "documentation": "https://www.elastic.co/guide/en/elasticsearch/reference/current/common-options.html",
+  "documentation": {
+    "url": "https://www.elastic.co/guide/en/elasticsearch/reference/current/common-options.html",
+    "description": "Parameters that are accepted by all API endpoints."
+  },

cc @Mpdreamz

[elasticmachine]

Pinging @elastic/es-core-infra