fix google_bigquery_table encryption_configuration modifications

- changing to/from CMEK requires recreating the table (see [Change a table from default encryption to Cloud KMS protection](https://cloud.google.com/bigquery/docs/customer-managed-encryption#change_to_kms))
- the BQ API appears to support the default -> kms transition (no API error), but tables don't appear to get encrypted according to the UI/CLI
- see hashicorp/terraform-provider-google#5241 and #2763 (comment) for more info

third_party/terraform/resources/resource_bigquery_table.go.erb

@@ -314,6 +314,7 @@ func resourceBigQueryTable() *schema.Resource {
 			"encryption_configuration": {
 				Type:     schema.TypeList,
 				Optional: true,
+				ForceNew: true,
 				MaxItems: 1,
 				Elem: &schema.Resource{
 					Schema: map[string]*schema.Schema{