Automatically detect the model signature

[fprost]

In the Model implementation, we do not guarantee that the model arguments are compatible with the CMLE model (in particular the signature of this model). Errors are spotted when collecting predictions after a batch prediction job.

It seems that this script has a potential solution (look for "(Optional) Inspect the model binaries with the SavedModel CLI ").

It would be a nice feature to help the user initialize a Model instance.

[fprost]

cc @msushkov