**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
"""
    Fetches the data from a BigQuery table (alternatively fetch data for selected columns)
    and returns data in a python list. The number of elements in the returned list will
    be equal to the number of rows fetched. Each element in the list will again be a list
    where element would represent the columns values for that row.
    **Example Result**: ``[['Tony', '10'], ['Mike', '20'], ['Steve', '15']]``
    .. seealso::
        For more information on how to use this operator, take a look at the guide:
        :ref:`howto/operator:BigQueryGetDataOperator`
    .. note::
        If you pass fields to ``selected_fields`` which are in different order than the
        order of columns already in
        BQ table, the data will still be in the order of BQ table.
        For example if the BQ table has 3 columns as
        ``[A,B,C]`` and you pass 'B,A' in the ``selected_fields``
        the data would still be of the form ``'A,B'``.
    **Example**: ::
        get_data = BigQueryGetDataOperator(
            task_id='get_data_from_bq',
            dataset_id='test_dataset',
            table_id='Transaction_partitions',
            max_results=100,
            selected_fields='DATE',
            gcp_conn_id='airflow-conn-id'
        )