**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
and_(
                        DatasetDagRunQueue.dataset_id == DatasetModel.id,
                        DatasetDagRunQueue.target_dag_id == DagScheduleDatasetReference.dag_id,
                    ),
                    isouter=True,
                )
                .join(
                    DatasetEvent,
                    and_(
                        DatasetEvent.dataset_id == DatasetModel.id,
                        DatasetEvent.timestamp > DatasetDagRunQueue.created_at,
                    ),
                    isouter=True,
                )
                .filter(DagScheduleDatasetReference.dag_id == dag_id, ~DatasetModel.is_orphaned)
                .group_by(DatasetModel.id, DatasetModel.uri)
                .order_by(DatasetModel.uri)
                .all()
            ]
        return (
            htmlsafe_json_dumps(data, separators=(",", ":"), dumps=flask.json.dumps),
            {"Content-Type": "application/json; charset=utf-8"},
        )
    @expose("/object/dataset_dependencies")
    @auth.has_access(
        [
            (permissions.ACTION_CAN_READ, permissions.RESOURCE_DAG_DEPENDENCIES),
        ]
    )
    def dataset_dependencies(self):