Support for lifting `F[_]: Concurrent` without related Data/DataSource into Fetch

This is a request for somewhat generalization of the issue brought up in https://github.com/47deg/fetch/issues/181
that was mentioned in the Gitter channel

as Fetch by itself requires `Concurrent` it'd be helpful to have a method like
```scala
def liftF[F[_]: Concurrent](ft: F[T]): Fetch[F, T]
```
to not be restricted for optimized flow for only `IO` monad