Support for `manual` camera prop (or configurable `onResize` canvas handler)

[davcri]

It would be handy in some case to manually control camera resize. I created a PR pmndrs/react-ogl#84 that could work for simpler cases.
However maybe it would be better to support something like r3f manual prop:

https://docs.pmnd.rs/react-three-fiber/tutorials/v8-migration-guide#manual-camera-manipulation