`analyze` should not prerender routes when specified via `routeRules`

[TheAlexLichter]

When analyzing a site via the analyze command, no prerendering should happen, even if routeRules: { '/**': { prerender: true } } or similar is set.

[pi0]

There is only one tricky case that some modules use prerender to emit assets that count in bundle size. But I think we can at least move --prerender behind a flag.