**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
"is_extra_encrypted",
    ]
    add_columns = [
        "conn_id",
        "conn_type",
        "description",
        "host",
        "schema",
        "login",
        "password",
        "port",
        "extra",
    ]
    edit_columns = add_columns.copy()
    
    extra_fields: list[str] = []
    add_form = edit_form = ConnectionForm
    add_template = "airflow/conn_create.html"
    edit_template = "airflow/conn_edit.html"
    add_widget = ConnectionFormWidget
    edit_widget = ConnectionFormWidget
    base_order = ("conn_id", "asc")
    extra_field_name_mapping: dict[str, str] = {}
    @action("muldelete", "Delete", "Are you sure you want to delete selected records?", single=False)
    @auth.has_access(
        [
            (permissions.ACTION_CAN_EDIT, permissions.RESOURCE_DAG),
        ]
    )
    def action_muldelete(self, items):