Add option to automatically expand schemas in SchemaDefinition to a certain level

I use <SchemaDefinition> to render my schemas. All my schemas are enveloped so that when the page is loaded, unfortunately nothing useful is shown, and it is not possible to use the browser's Find-In-Page to search for useful properties. All the interesting stuff is "one level down".

I currently work around this by executing the following in the Redoc.init callback:

var els = document.querySelectorAll('td button');
for (el of els) {
  el.click();
}
// Needed because expansion shifts the browser view
setTimeout(function () { window.location.hash = window.location.hash; })

This is, of course, just a hack and not in any way optimal.

It would be nice if ReDoc supported automatically expanding SchemaDefinition nodes to a certain level.

Note that #1693 would solve this fairly elegantly.

Start at the SchemaDefinition component and its expansion controls, then compare the requested behavior with the approach mentioned in #1693. Done means ReDoc exposes a configurable expansion depth so enveloped schemas show useful nested properties on initial load without the DOM-click workaround.