**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
filter(None, [record["start_date"], ti_summary.start_date]), default=None
                    )
                    record["end_date"] = max(
                        filter(None, [record["end_date"], ti_summary.end_date]), default=None
                    )
                    record["mapped_states"][ti_summary.state] = ti_summary.state_count
                if record:
                    set_overall_state(record)
                    yield record
            if isinstance(item, MappedOperator) or is_parent_mapped:
                instances = list(_mapped_summary(grouped_tis.get(item.task_id, [])))
            else:
                instances = list(map(_get_summary, grouped_tis.get(item.task_id, [])))
            return {
                "id": item.task_id,
                "instances": instances,
                "label": item.label,
                "extra_links": item.extra_links,
                "is_mapped": isinstance(item, MappedOperator) or is_parent_mapped,
                "has_outlet_datasets": any(isinstance(i, Dataset) for i in (item.outlets or [])),
                "operator": item.operator_name,
            }
        
        task_group = item
        group_is_mapped = isinstance(task_group, MappedTaskGroup)
        children = [
            task_group_to_grid(child, grouped_tis, is_parent_mapped=group_is_mapped)
            for child in task_group.topological_sort()
        ]
        def get_summary(dag_run: DagRun):