[BUG] WebHook notification with json body

[DmitriiKuvshinov]

What is the bug?
I want to send webhooks to our Rocket.Chat, but OpenSearch send html body, not json

How can one reproduce the bug?
Configuration of notification

{
  "start_index" : 0,
  "total_hits" : 1,
  "total_hit_relation" : "eq",
  "config_list" : [
    {
      "config_id" : "Ip75-5IBkTxtk5bkXEfE",
      "last_updated_time_ms" : 1730808888085,
      "created_time_ms" : 1730804276420,
      "config" : {
        "name" : "Rocket",
        "description" : "",
        "config_type" : "webhook",
        "is_enabled" : true,
        "webhook" : {
          "url" : "https://rocket.domain/hooks/**webhook**",
          "header_params" : {
            "Content-Type" : "application/json"
          },
          "method" : "PUT"
        }
      }
    }
  ]
}

What is the expected behavior?
A clear and concise description of what you expected to happen.

What is your host/environment?

• OS: Ubuntu Server 22.04
• OpenSearch 2.17.1

Do you have any screenshots?