Add basic support for hotwired/turbo in the backend

[m-vo]

This is the first attempt to add Turbo in the backend. This does not yet enable frames or uses streams at any place but enables drive by default. We will likely need to disable it by default and then enable it again for specific scenarios but this is a good starting point to see what would actually break.

For now these are the things we are doing:

• Disable prefetch for all URLs that contain a rt query parameter, so that things like GET requests to delete resources won't be triggered.
• Change the returned status code to 422 in the BackendController if a widget was rendered with an error, so that forms still work.
• Disable it for the login form (because it's a completely different structure).
• t.b.c.

[fritzmg]

There are two issues that I noticed:

• When going from any page to the file manager, there will be a JS error regarding DropZone. This is because the DropZone JavaScript is only added there - which is ignored by Turbo by default (without data-turbo-track="reload").
• For some reason the navigations panes in the main nav are getting toggled randomly sometimes, when navigating with Turbo Drive.

[fritzmg]

We also need to change all form.submit() calls with form.requestSubmit() in order for these form submits to be turböd.