Report error message in helm when required configs are not set

[mwylde]

A kubernetes/helm deployment of Arroyo has two required config values that must be set:

• checkpointUrl — specifies a path/object store URL for checkpoint storage
• artifactURL — specifies a path/object store URL for compilation artifacts (UDF dylibs)

For example, a valid helm config running on AWS might look like this:

artifactUrl: "s3://arroyo-artifacts"
checkpointUrl: "s3://arroyo-checkpoints"

However, if the user doesn't specify these configs the helm chart will still deploy, but the controller pod will crash on startup with an error message.

It would be a better user experience to fail the helm deployment if these required configs are not set.