Support more prefetch configuration options (#92859)
"auto" mode is the default. It does not need to be explicitly exported
"force-" modes suggest overriding framework heuristics "force-disabled"
disables prefetching for this segment "force-static" forces any
prefetching of this segment to be static "force-runtime" forces any
prefetching of this segment to do runtime prefetching
It's worth noting that when runtime prefetching we fetch the necessary
segment and all child segments in a single request. This means that a
deeper segment might specify disabled or static and still get
conditionally rendered as a runtime prefetch. This was already the
behavior of runtime prefetching and not changing in this PR just
something to call out since it may be confusing to folks trying to
understand how the implementation of prefetching actually work
