[fix] reestablish prerender.enabled option

[dummdidumm]

fixes #7899
I figured this is the easiest and most straightforward fix to the issue. That option still makes sense to have even after the prerendering->building change, which is somewhat orthogonal. We still reserve the right to load the files at build time and look at a potential config option, we just added back the additional granularity of disabling prerendering altogether.

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[dummdidumm]

Discussed offline - we think it's better to establish some kind of adapter method for this instead.