**Apache Airflow version**: 2.1.1

**What happened**:

The rendered templates screen doesn't show the operator arguments for TaskFlow API operators.
![image](https://user-images.githubusercontent.com/72943478/125486179-f6dde0be-9f60-4aca-831a-5cfd16e7f006.png)

**What you expected to happen**:

Should show the arguments after any templates have been rendered.

**How to reproduce it**:

Will happen for any `@task` decorated operator.

**Anything else we need to know**:

This issue appears on a number of operators.  Possible solution is to modify the "get_python_source" in utils/code_utils.py to handle list and dict. This would cause any operator that using py as the renderer to handle lists and dicts.  Possibly something like:
```
    if isinstance(x, list):
        return [str(v) for v in x]

    if isinstance(x, dict):
        return {k: str(v) for k, v in x.items()}
```
The converting values to strings seems necessary in order to avoid errors when this is passed to the pygments lexer.
![image](https://user-images.githubusercontent.com/72943478/125494716-01cf0c11-9e5f-45fa-afe2-4f99409edefc.png)

airflow/www/views.py
"""Triggers DAG Run."""
        dag_id = request.values.get('dag_id')
        origin = get_safe_url(request.values.get('origin'))
        request_conf = request.values.get('conf')
        request_execution_date = request.values.get('execution_date', default=timezone.utcnow().isoformat())
        if request.method == 'GET':
            
            default_conf = ''
            dag = current_app.dag_bag.get_dag(dag_id)
            doc_md = wwwutils.wrapped_markdown(getattr(dag, 'doc_md', None))
            form = DateTimeForm(data={'execution_date': request_execution_date})
            if request_conf:
                default_conf = request_conf
            else:
                try:
                    default_conf = json.dumps(dag.params, indent=4)
                except TypeError:
                    flash("Could not pre-populate conf field due to non-JSON-serializable data-types")
            return self.render_template(
                'airflow/trigger.html',
                dag_id=dag_id,
                origin=origin,
                conf=default_conf,
                doc_md=doc_md,
                form=form,