**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
:param source_objects: List of Google Cloud Storage URIs to point
        table to. If source_format is 'DATASTORE_BACKUP', the list must only contain a single URI.
    :type source_objects: list
    :param destination_project_dataset_table: The dotted ``(<project>.)<dataset>.<table>``
        BigQuery table to load data into (templated). If ``<project>`` is not included,
        project will be the project defined in the connection json.
    :type destination_project_dataset_table: str
    :param schema_fields: If set, the schema field list as defined here:
        https://cloud.google.com/bigquery/docs/reference/rest/v2/jobs#configuration.load.schema
        **Example**: ::
            schema_fields=[{"name": "emp_name", "type": "STRING", "mode": "REQUIRED"},
                           {"name": "salary", "type": "INTEGER", "mode": "NULLABLE"}]
        Should not be set when source_format is 'DATASTORE_BACKUP'.
    :param table_resource: Table resource as described in documentation:
        https://cloud.google.com/bigquery/docs/reference/rest/v2/tables#Table
        If provided all other parameters are ignored. External schema from object will be resolved.
    :type table_resource: Dict[str, Any]
    :type schema_fields: list
    :param schema_object: If set, a GCS object path pointing to a .json file that
        contains the schema for the table. (templated)
    :type schema_object: str
    :param source_format: File format of the data.
    :type source_format: str
    :param compression: [Optional] The compression type of the data source.
        Possible values include GZIP and NONE.
        The default value is NONE.
        This setting is ignored for Google Cloud Bigtable,
        Google Cloud Datastore backups and Avro formats.
    :type compression: str
    :param skip_leading_rows: Number of rows to skip when loading from a CSV.