MonadControl instance for Process.

A `MonadControl` instance makes it possible to lift many actions with an
occurrence of `IO` in negative position to the `Process` monad. See e.g.
the async library, which contains many such actions. This patch makes it
possible to use `async` with `distributed-process`, via `lifted-async`.

Signed-off-by: Mathieu Boespflug <m@tweag.io>