**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. 🚀 


airflow/www/views.py
Markup(
                    "Usage of <b>SequentialExecutor</b> detected. "
                    "Do not use <b>SequentialExecutor</b> in production. "
                    f"<a href='{exec_doc_page}'><b>Click here</b></a> for more information."
                ),
                category="warning",
            )
        hide_paused_dags_by_default = conf.getboolean('webserver', 'hide_paused_dags_by_default')
        default_dag_run = conf.getint('webserver', 'default_dag_run_display_number')
        num_runs = request.args.get('num_runs', default=default_dag_run, type=int)
        current_page = request.args.get('page', default=0, type=int)
        arg_search_query = request.args.get('search')
        arg_tags_filter = request.args.getlist('tags')
        arg_status_filter = request.args.get('status')
        if request.args.get('reset_tags') is not None:
            flask_session[FILTER_TAGS_COOKIE] = None
            
            return redirect(url_for('Airflow.index'))
        cookie_val = flask_session.get(FILTER_TAGS_COOKIE)
        if arg_tags_filter:
            flask_session[FILTER_TAGS_COOKIE] = ','.join(arg_tags_filter)
        elif cookie_val:
            
            return redirect(url_for('Airflow.index', tags=cookie_val.split(',')))
        if arg_status_filter is None:
            cookie_val = flask_session.get(FILTER_STATUS_COOKIE)
            if cookie_val:
                arg_status_filter = cookie_val
            else:
                arg_status_filter = 'active' if hide_paused_dags_by_default else 'all'