Add index mode to resolve index response.

[seanzatzdev]

This PR adds the index mode in the resolve index action response, and resolves this issue: #110382

e.g.

{
    "indices": [
        {
            "name": "blogs",
            "attributes": [
                "open"
            ],
            "mode": "standard"
        }
    ],
    "aliases": [],
    "data_streams": []
}

[elasticsearchmachine]

Pinging @elastic/es-data-management (Team:Data Management)

[elasticsearchmachine]

Hi @seanzatzdev, I've created a changelog YAML for you.

[masseyke]

I left a couple of comments, but it look good to me.