manifest: put back `transport` property to the Manifest
manifest: put back `transport` property to the Manifest

It turns out the `transport` property, which was just removed because it
should not be useful on a Manifest structure, is actually defined in the
API (for typing the Manifest structure).

This force us to put it back if we do not want to bring a breaking
change.

canalplus/rx-player,canalplus/rx-player,canalplus/rx-player,canalplus/rx-player,canalplus/rx-player