undocumented `resource` field in the `/rate_limit` endpoint

[skedwards88]

In some cases, a request to the /rate_limit endpoint returns a resource field for each resources object:

{
  "resources": {
    "core": {
      "limit": 15000,
      "used": 0,
      "remaining": 15000,
      "reset": 1704236754,
      "resource": "core" // returned in some cases but not documented
    },
...
}

(Note that this resource field is not returned with an authenticated gh api request but is returned with an unauthenticated request to https://api.github.com/rate_limit.)

However, this resource field is not documented. We should:

• omit this field from the response
  OR
• add this field to the schema and note that it is not always returned (the docs will automatically update once the schema is updated)

For internal discussion, see here and here.

[JLLeitschuh]

The reason I ran into this was because auto-generated code against the schema breaks Jackson's JSON parser when executed in it's default mode, which is to fail when JSON fields aren't explicitly specified, but are present in the data it's attempting to deserialize from.