Live Preview option to automatically add a time-limited token to the query (incl. ENV vars)

Summary _Provide an easy way to (live) preview apps/sites that use unpublished and protected data._ In the data model settings of a collection we can specify a Preview URL. It would be nice if we could add a temporary authentication token to this URL, so that the front-end application can access unpublished data via the API with a time-limited access token. In addition, it would be nice if we could set the base URL for the Preview URL as an ENV variable (like PROJECT_URL), so that when a relative Preview URL is specified, this base URL (PROJECT_URL) will be taken. Basic Example I have already created an endpoint extension that does just that: [Tokenized Preview Endpoint]( Motivation The ability to attach a time-limited token to the Preview URL allows a front-end application to access content/data that is not publicly accessible via the API. This is basically the main reason why I want to preview an item. Setting the base URL as an ENV variable, as described abo…