**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
"""
    Cast the task_duration to an int was for optimization for large/huge dags if task_duration > 10s
    otherwise we keep it as a float with 3dp
    """
    return int(task_duration) if task_duration > 10.0 else round(task_duration, 3)
def sanitize_args(args: dict[str, str]) -> dict[str, str]:
    """
    Remove all parameters starting with `_`
    :param args: arguments of request
    :return: copy of the dictionary passed as input with args starting with `_` removed.
    """
    return {key: value for key, value in args.items() if not key.startswith("_")}
def get_safe_url(url):
    """Given a user-supplied URL, ensure it points to our web server"""
    if not url:
        return url_for("Airflow.index")
    
    
    if ";" in unquote(url):
        return url_for("Airflow.index")
    host_url = urlsplit(request.host_url)
    redirect_url = urlsplit(urljoin(request.host_url, url))
    if not (redirect_url.scheme in ("http", "https") and host_url.netloc == redirect_url.netloc):
        return url_for("Airflow.index")
    
    return redirect_url.geturl()
def get_date_time_num_runs_dag_runs_form_data(www_request, session, dag):