Support batch prediction

[jlewi]

We'd like fairing to support batch prediction.

See also #38 support deploying models.

we'd like to be able to fire of a batch predict job from a notebook using fairing.

As in online predict (#38) there are likely two cases

1. TF model
2. Non TF model

In the case of #1 we can probably use our existing Beam transform for doing batch predict using a saved model.

In the case of #2 the user probably needs to write a batch_predict method that can then be invoked.

We should consider whether to use beam to parallelize the computation or maybe just fire off a bunch of K8s jobs.

[jtfogarty]

/area engprod /kind feature