Fix S3 Version Type

The Version type of the Concourse-native S3 resource depends on whether the resource is configured as a versioned file, i.e. whether the underlying S3 object is versioned, in which case the type { version_id : Text } is used, or whether the resource is configured as a regular expression which extracts the version from the name of an object, in which case the type { path : Text } is used.

The code had mistakenly assumed that only versioned objects, i.e. { version_id : Text }, were possible. This misunderstanding has been fixed by replacing the Version type with a union that allows either { version_id : Text } or { path : Text }, so that now S3 objects whose version is of type { path : Text } can be pinned.