Create a `InputService` class with an abstract method called `map`,
meant to be implemented by all inputs. An `unmap` method may be
optionally overridden by inputs to cleanup resources.
Instantiate a `host.ServiceManager` in the `Stage.run` section and
pass the to the host side input code so it can be used to spawn the
input services.
Convert all existing inputs to the new service framework.
Instead of bind-mounting each individual input into the container,
create a temporary directory that is used by all inputs and bind-
mount this to the well known location ("/run/osbuild/inputs"). The
temporary directory is then passed to the input so that it can
make the requested resources available relative to that directory.
This is enforced by the common input handling code.
Additionally, pass the well known input path via a new "paths" key
to the arguments dictionary passed to the stage.
