**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
"""
    Update BigQuery Table Schema
    Updates fields on a table schema based on contents of the supplied schema_fields_updates
    parameter. The supplied schema does not need to be complete, if the field
    already exists in the schema you only need to supply keys & values for the
    items you want to patch, just ensure the "name" key is set.
    .. seealso::
        For more information on how to use this operator, take a look at the guide:
        :ref:`howto/operator:BigQueryUpdateTableSchemaOperator`
    :param schema_fields_updates: a partial schema resource. see
        https://cloud.google.com/bigquery/docs/reference/rest/v2/tables#TableSchema
    **Example**: ::
        schema_fields_updates=[
            {"name": "emp_name", "description": "Some New Description"},
            {"name": "salary", "policyTags": {'names': ['some_new_policy_tag']},},
            {"name": "departments", "fields": [
                {"name": "name", "description": "Some New Description"},
                {"name": "type", "description": "Some New Description"}
            ]},
        ]
    :type schema_fields_updates: List[dict]
    :param include_policy_tags: (Optional) If set to True policy tags will be included in
        the update request which requires special permissions even if unchanged (default False)
        see https://cloud.google.com/bigquery/docs/column-level-security#roles
    :type include_policy_tags: bool
    :param dataset_id: A dotted
        ``(<project>.|<project>:)<dataset>`` that indicates which dataset