Page REST endpoint supports content rendering as fallback

A new supportedSyntax query parameter has been added to the REST API endpoint for pages.

A client can use it to list all the syntaxes it supports. If the page is using a syntax that was not part of the list in the request, the response will now include a renderedContent property that the client will be able to use as a fallback instead of the raw content it can't handle.
If this parameter is omitted, no rendered content will be added to the response.