Support generate dynamic sitemaps for dynamic routes (#48867)
### What
For dynamic routes you might have different sitemap for different params
* Unloack using `sitemap.[ext]` in your app everywhere
* Support `generateSitemaps()` to create multiple sitemaps at the same time
### How
* Change the metadata regex to allow use sitemap in every routes
* Similar approach to `generateImageMetadata`, we make `sitemap.js` under dynamic routes to a catch all routes, and it can have multiple routes
Closes NEXT-1054
