prerender: hooks

[pi0]

nuxt/nuxt#11786

Most importantly prerender:route hook which can be useful to modify and inspect pretender results. (eg: for service-worker to inject it's script)

[farnabaz]

We have a prerender:route hoo, but it is not useful. (Changing route data does not affect on generated content)
https://github.com/unjs/nitro/blob/cbc7ba3835df539116ca6560a85365615af55fbb/src/prerender.ts#L99

But this should move into generateRoute function, before persisting content into file

https://github.com/unjs/nitro/blob/cbc7ba3835df539116ca6560a85365615af55fbb/src/prerender.ts#L66-L68

WDYT @pi0

[pi0]

Nice find @farnabaz. prerender:route is called outside as for generic error handling and stats purposes. We might introduce another predenrer hook and use before writeFileCall to allow extending to skipping.