**Description**

Replace the Configuration JSON text-area with a form that has individual input fields for each key & value. This will remove the need for the user to provide a json object. See hashicorp vault's key-value secrets UI for an example of what this might look like:

![Screenshot 2020-09-21 at 12 06 03](https://user-images.githubusercontent.com/17148324/93759844-df04f680-fc02-11ea-8613-f3bcc0b22d09.png)
 
- If present these keys and values should be serialised as json client-side and posted to the trigger-dag API endpoint as the `conf` request-parameter.
- By default no conf request-parameter is sent. Perhaps a checkbox should be used to determine whether conf is sent at all?
- The user may want to add new keys, or remove keys & values that they have previously added.
- [PR-10839](https://github.com/apache/airflow/pull/10839) is pre-populating the form with the DAG's default params. The new form should be pre-populated with the keys & values from `DAG.params`


**Use case / motivation**

Currently when triggering a manual DAG run with user-provided runtime parameters, the user has to provide a correctly formatted JSON object. Filling in a form with keys & values will be a significantly better user experience, and will be less error prone & laborious than handling json in a free-text field.

This builds on the great work already done on enhancing the Trigger-DAG functionality

**Related Issues**

Originating PR: https://github.com/apache/airflow/pull/10839
if get_airflow_app().appbuilder.sm.has_all_dags_access(g.user):
            return query
        filter_dag_ids = get_airflow_app().appbuilder.sm.get_accessible_dag_ids(g.user)
        return query.filter(self.model.dag_id.in_(filter_dag_ids))
class AirflowModelView(ModelView):
    """Airflow Mode View.
    Overridden `__getattribute__` to wraps REST methods with action_logger
    """
    list_widget = AirflowModelListWidget
    page_size = PAGE_SIZE
    CustomSQLAInterface = wwwutils.CustomSQLAInterface
    def __getattribute__(self, attr):
        """Wraps action REST methods with `action_logging` wrapper
        Overriding enables differentiating resource and generation of event name at the decorator level.
        if attr in ["show", "list", "read", "get", "get_list"]:
            return action_logging(event="RESOURCE_NAME"."action_name")(attr)
        else:
            return attr
        """
        attribute = object.__getattribute__(self, attr)
        if (
            callable(attribute)
            and hasattr(attribute, "_permission_name")
            and attribute._permission_name in self.method_permission_name
        ):
            permission_str = self.method_permission_name[attribute._permission_name]
            if permission_str not in ["show", "list", "read", "get", "get_list"]:
                return action_logging(event=f"{self.route_base.strip('/')}.{permission_str}")(attribute)
        return attribute
class AirflowPrivilegeVerifierModelView(AirflowModelView):