**Description**

`BigQueryInsertJobOperator` requires the submission of a `configuration` parameter in the form of a dict.  Unfortunately, if this contains a large SQL query - especially one that is formatted with new lines - then this cannot currently be rendered very nicely in the UI.

<img width="1670" alt="Screenshot 2021-07-15 at 15 39 33" src="https://user-images.githubusercontent.com/967119/125806943-839d57a9-d4a0-492d-b130-06432b095239.png">

**Use case / motivation**

The issue with this is that it's impossible to copy and paste the rendered query out of the Airflow UI, into a BigQuery browser and run it without lots of manual edits which is time wasted when troubleshooting problems.

**Are you willing to submit a PR?**

Yes.  My current thought process around this would be to add an optional SQL parameter to the operator which, if provided, would be added into the configuration and could therefore have its own template field and SQL renderer.

e.g.

<img width="1570" alt="Screenshot 2021-07-14 at 14 18 09" src="https://user-images.githubusercontent.com/967119/125808200-5f30b8f4-4def-48a7-8223-82afdc65c973.png">


airflow/providers/google/cloud/operators/bigquery.py
labels: Optional[Dict] = None,
        view: Optional[Dict] = None,
        materialized_view: Optional[Dict] = None,
        encryption_configuration: Optional[Dict] = None,
        location: Optional[str] = None,
        cluster_fields: Optional[List[str]] = None,
        impersonation_chain: Optional[Union[str, Sequence[str]]] = None,
        exists_ok: bool = False,
        **kwargs,
    ) -> None:
        super().__init__(**kwargs)
        self.project_id = project_id
        self.dataset_id = dataset_id
        self.table_id = table_id
        self.schema_fields = schema_fields
        self.gcs_schema_object = gcs_schema_object
        self.bigquery_conn_id = bigquery_conn_id
        self.google_cloud_storage_conn_id = google_cloud_storage_conn_id
        self.delegate_to = delegate_to
        self.time_partitioning = {} if time_partitioning is None else time_partitioning
        self.labels = labels
        self.view = view
        self.materialized_view = materialized_view
        self.encryption_configuration = encryption_configuration
        self.location = location
        self.cluster_fields = cluster_fields
        self.table_resource = table_resource
        self.impersonation_chain = impersonation_chain
        self.exists_ok = exists_ok
    def execute(self, context) -> None: