Consider attaching RefreshLess even when no session exists/user is anonymous

Problem/Motivation

To quote the Turbo handbook:

A key attraction with traditional single-page applications, when compared with the old-school, separate-pages approach, is the speed of navigation. SPAs get a lot of that speed from not constantly tearing down the application process, only to reinitialize it on the very next page.

On a more complex site, I would argue that the benefits of the RefreshLess approach outweigh the benefits of relying on the page cache for anonymous users and provide a more consistent/better UX.

Steps to reproduce

Try RefreshLess while not logged in to a site.

Proposed resolution

Either remove the check for a session in \refreshless_page_attachments() or add a configuration setting that sites can use to opt into or out of RefreshLess for anonymous users. Maybe even set the default to allow RefreshLess for anonymous users. If this conflicts with the BigPipe module, maybe add a check for that?

Remaining tasks

Do the thing.

User interface changes

Possibly add a configuration form?

API changes

Config I think?

Data model changes

Unsure.