Add `in` and `check` script

[DanielJonesEB]

Would it be of use to anyone else to have a check that emitted a version that was some sort of hash of app bits and (generated) app manifest, along with an in to get both?

It'd be nice to drive pipelines a bit more semantically by knowing when an app has changed, rather than relying on passing whatever caused that change to propagate down the pipeline.

[cromega]

@DanielJonesEB I would love to see this functionality. would be nice to pass the metadata to subsequent jobs (for running smoke tests against a deployment for example)