19300 fix

[kumardeepak5]

Purpose

Resolves wso2/product-is#19300

Goals

This PR eliminates an unnecessary error log when a user tries to add an email template type that already exists in the system.

Behavior After Fix:
Sample Request:

curl --location 'https://localhost:9443/t/carbon.super/api/server/v1/email/template-types' \
--header 'Content-Type: application/json' \
--header 'Authorization: Basic <username:password>' \
--data '{
  "displayName": "Account Confirmation1",
  "templates": [
    {
      "contentType": "text/html",
      "subject": "WSO2 - Account Confirmation",
      "body": "HTML Body",
      "footer": "WSO2 Identity Server Team",
      "id": "en_US1"
    }
  ]
}'

Sample Response
Response Code - 409

{
    "code": "ETM-50005",
    "message": "Email Template Type already exists in the system.",
    "description": "An email template type for the provided template display name already exists in the system.",
    "traceId": "91104c8e-731b-40de-9a3b-4cb178f0c755"
}