**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
return redirect(self.get_default_url())
def action_has_dag_edit_access(action_func: Callable) -> Callable:
    """Decorator for actions which verifies you have DAG edit access on the given tis/drs."""
    @wraps(action_func)
    def check_dag_edit_acl_for_actions(
        self,
        items: list[TaskInstance] | list[DagRun] | TaskInstance | DagRun | None,
        *args,
        **kwargs,
    ) -> Callable:
        if items is None:
            dag_ids: set[str] = set()
        elif isinstance(items, list):
            dag_ids = {item.dag_id for item in items if item is not None}
        elif isinstance(items, TaskInstance) or isinstance(items, DagRun):
            dag_ids = {items.dag_id}
        else:
            raise ValueError(
                "Was expecting the first argument of the action to be of type "
                "list[TaskInstance] | list[DagRun] | TaskInstance | DagRun | None."
                f"Was of type: {type(items)}"
            )
        for dag_id in dag_ids:
            if not get_airflow_app().appbuilder.sm.can_edit_dag(dag_id):
                flash(f"Access denied for dag_id {dag_id}", "danger")
                logging.warning("User %s tried to modify %s without having access.", g.user.username, dag_id)
                return redirect(self.get_default_url())
        return action_func(self, items, *args, **kwargs)
    return check_dag_edit_acl_for_actions