[DOCS] Add overlays to work around deployment failure

[lcawl]

The Elasticsearch OpenAPI document for the main and 9.0 branches and the Elasticsearch Serverless OpenAPI document for the main branch cannot be deployed successfully on our publishing site.

This issue tracks the work-arounds necessary to get that content published.

Per feedback from Bump.sh, the problematic part of the documents is:

"_types:ScriptSource":

{ "oneOf": [

{ "type": "string" },

{ "$ref": "#/components/schemas/_global.search._types:SearchRequestBody" }

]

In particular, if the $ref is deleted, the file can be deployed successfully.

In the 8.18 branch, this schema item does not exist. Rather, the source was treated as a string. For example:

      "_types.Script": {
        "type": "object",
        "properties": {
          "source": {
            "description": "The script source.",
            "type": "string"
          },

The change to also support the _global.search._types:SearchRequestBody seems related to #2960