move ResourceInventory and inventory modules from KC to pkg

[jack-evans]

I was looking into kustomize-controller and was wondering if it would be beneficial to move the ResourceInventory (in the API) and inventory modules into fluxcd/pkg?

These seem like they would be really useful for other developers looking to build their own controllers/operators built on top of flux (or in general) with the capabilities to prune and keep a track record of resources deployed for a given CR.