Remove mutation of `renderOpts` (#54888)
It's a bad pattern to do things like `(renderOpts as any).fetchMetrics = staticGenerationStore.fetchMetrics` and receive the updated value in the outside. This PR updates it to use `RenderResults`'s metadata instead.
In the future we should use `Reaedonly<RenderOpts>` and ban `as any` <picture data-single-emoji=":lolsob:" title=":lolsob:"><img class="emoji" width="20" height="auto" src="https://emoji.slack-edge.com/T0CAQ00TU/lolsob/2e754996aebc14fa.png" alt=":lolsob:" align="absmiddle"></picture>
