**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
"""View to provide autocomplete results"""
    @auth.has_access([(permissions.ACTION_CAN_READ, permissions.RESOURCE_DAG)])
    @provide_session
    @expose("/dagmodel/autocomplete")
    def autocomplete(self, session=None):
        """Autocomplete."""
        query = unquote(request.args.get("query", ""))
        if not query:
            return flask.json.jsonify([])
        
        dag_ids_query = session.query(
            sqla.literal("dag").label("type"),
            DagModel.dag_id.label("name"),
        ).filter(~DagModel.is_subdag, DagModel.is_active, DagModel.dag_id.ilike("%" + query + "%"))
        owners_query = (
            session.query(
                sqla.literal("owner").label("type"),
                DagModel.owners.label("name"),
            )
            .distinct()
            .filter(~DagModel.is_subdag, DagModel.is_active, DagModel.owners.ilike("%" + query + "%"))
        )
        
        status = flask_session.get(FILTER_STATUS_COOKIE)
        if status == "active":
            dag_ids_query = dag_ids_query.filter(~DagModel.is_paused)
            owners_query = owners_query.filter(~DagModel.is_paused)
        elif status == "paused":