BigQuery feature: support determinism level for javascript UDFs

[shollyman]

Summary

Ensure BigQuery client library supports the ability for a javascript UDF (exposed via the Routine resource) to communicate determinism level.

The functionality here is to allow users to inform the query engine about whether a function is deterministic or not, which can improve query performance. Existing clients should already support the routines methods and resource type, so this should largely be a case of exposing a new field of the Routine and updating existing testing.

For integration testing, please note that only javascript UDFs allow determinism to be set; the backend will likely error when you try to set determinism for SQL UDFs or stored procedures.

References

Public REST reference includes information about the routine resource structure:

https://cloud.google.com/bigquery/docs/reference/rest/v2/routines#resource:-routine

Here's an example implementation that adds a new field to the Routine resource type in Go:

googleapis/google-cloud-go#3534