feat: add storage_billing_model and default_partition_expiration_ms

[SamuZad]

This closes https://github.com/terraform-google-modules/terraform-google-bigquery/issues/235 (which previously had a PR that was cancelled) and https://github.com/terraform-google-modules/terraform-google-bigquery/issues/333

Adds the option to specify storage_billing_model Also adds in validation for storage_billing_model Adds the option to specify default_partition_expiration_ms

Regarding validation, I've wanted to preserve the default behaviour of the underlying terraform resource so the default of storage_billing_model is null. This is to make the addition of this variable as seamless as possible. However, this means that I can't use the contains function to validate the variable, as contains() errors out if what it checks is null