Add support for Template block

[KoditkarVedant]

Notion has added support for adding and retrieving template block types. Using this block type, developers can now create template that duplicates the its children blocks.

Below is an example request body for the append block children endpoint containing a template block type.

Template block type used in request body

{
    "children": [
        {
            "type": "template",
            "template": {
                "text": [
                    {
                        "type": "text",
                        "text": {
                            "content": "Create callout template"
                        }
                    }
                ],
                "children": [
                    {
                        "callout": {
                            "text": [
                                {
                                    "type": "text",
                                    "text": {
                                        "content": "Placeholder callout text"
                                    }
                                }
                            ]
                        }
                    }
                ]
            }
        }
    ]
}

Notion API changelog: https://developers.notion.com/changelog/synced-block-link-to-page-and-template-block-types-are-now-supported-in-the-api