Add SqlJob and Flink Streaming impl

[ryannedolan]

Summary

Add SqlJob CRD and Flink Streaming implementation.

Details

The new SqlJob CRD provides a generic API for SQL-based jobs. So far, Flink SQL in Streaming mode is supported.

For now, Subscriptions do not create SqlJobs, but instead create FlinkDeployments directly.

Testing Done

$ kubectl apply -f deploy/samples/sqljobs.yaml

$ kubectl get sqljobs                                                                                   
NAME          DIALECT   MODE        STATUS
hello-world   Flink     Streaming   Ready.