Document preview and secure Access

[Simply007]

Motivation

Extend the boilerplate by providing information about connection delivery client o the preview data from Kentico Cloud delivery endpoint.

• Implementation is already prepared

Proposed solution

• Extend the config file by properties for secured and preview functionality like that:

{
***
  "deliveryConfig" : {
    ***
    "enablePreviewMode": false,
    "previewApiKey": "",
    "enableSecuredMode": false,
    "securedApiKey": ""
    ***
  }
***
}

• Document configuration in Readme

Additional context

• https://developer.kenticocloud.com/docs/previewing-content-in-a-separate-environment#section-using-the-delivery-preview-api
• https://developer.kenticocloud.com/reference#secure-access