Add a lightweight apache::site resource

Learn from the past and avoid creating a whiz-bang resource that tries to do
too much. Instead, introduce a very lightweight apache::site that is little
more than a thin wrapper around a file resource. Compared to a bare file
resource, using apache::site will give you filename normalization and automatic
dependencies and notifications.

Change-Id: I354355ef5c7c1d5a94f19680a04486c06fff1d95