**Apache Airflow version**:
2.1.0

**What happened**:
There are several hooks that still use optional parameters from the classic `Extra` field.  However, when creating the connection the `Extra` field is overwritten with values from the custom fields that are included in the form.  Because the `Extra` field is overwritten, these optional parameters cannot be used by the hook.

For example, in the `AzureDataFactoryHook`, If `resource_group_name` or `factory_name` are not provided when initializing the hook, it defaults to the value specified in the connection extras. Using the Azure Data Factory connection form, here is the initial connection submission:
![image](https://user-images.githubusercontent.com/48934154/127029091-a8b1c979-f238-4bac-9d3a-f94b6cd92a2b.png)

After saving the connection, the `Extra` field is overwritten with the custom fields that use "extras" under the hood:
![image](https://user-images.githubusercontent.com/48934154/127029242-79c990f0-b9cf-43bb-9a6b-28b4e9c6d4e1.png)


**What you expected to happen**:

Wavering slightly but I would have initially expected that the `Extra` field wasn't overwritten but updated with both the custom field "extras" plus the originally configured values in the `Extra` field.  However, a better UX would be that the values used in the `Extra` field should be separate custom fields for these hooks and the `Extra` field is hidden.  Perhaps it's even both?

**How to reproduce it**:
Install either the Microsoft Azure or Snowflake providers, attempt to create a connection for either the Snowflake, Azure Data Factory, Azure Container Volume, or Azure types with the `Extra` field populated prior to saving the form.


**Anything else we need to know**:
Happy to submit PRs to fix this issue. 🚀 


tests/www/views/test_views_connection.py
description='MongoDB2',
        host='localhost',
        schema='airflow',
        port=3306,
    )
    conn3 = Connection(
        conn_id='test_duplicate_postgres_connection_copy1',
        conn_type='FTP',
        description='Postgres',
        host='localhost',
        schema='airflow',
        port=3306,
    )
    with create_session() as session:
        session.query(Connection).delete()
        session.add_all([conn1, conn2, conn3])
        session.commit()
    data = {"action": "mulduplicate", "rowid": [conn1.id, conn3.id]}
    resp = admin_client.post('/connection/action_post', data=data, follow_redirects=True)
    expected_result = {
        'test_duplicate_gcp_connection',
        'test_duplicate_gcp_connection_copy1',
        'test_duplicate_mysql_connection',
        'test_duplicate_postgres_connection_copy1',
        'test_duplicate_postgres_connection_copy2',
    }
    response = {conn[0] for conn in session.query(Connection.conn_id).all()}
    assert resp.status_code == 200
    assert expected_result == response