### Apache Airflow version

2.1.3

### Operating System

ContainerOS

### Versions of Apache Airflow Providers

apache-airflow-providers-amazon==2.1.0
apache-airflow-providers-celery==2.0.0
apache-airflow-providers-cncf-kubernetes==2.0.2
apache-airflow-providers-databricks==2.0.1
apache-airflow-providers-docker==2.1.0
apache-airflow-providers-elasticsearch==2.0.2
apache-airflow-providers-ftp==2.0.0
apache-airflow-providers-google==5.0.0
apache-airflow-providers-grpc==2.0.0
apache-airflow-providers-hashicorp==2.0.0
apache-airflow-providers-http==2.0.0
apache-airflow-providers-imap==2.0.0
apache-airflow-providers-microsoft-azure==3.1.0
apache-airflow-providers-mysql==2.1.0
apache-airflow-providers-papermill==2.0.1
apache-airflow-providers-postgres==2.0.0
apache-airflow-providers-redis==2.0.0
apache-airflow-providers-sendgrid==2.0.0
apache-airflow-providers-sftp==2.1.0
apache-airflow-providers-slack==4.0.0
apache-airflow-providers-sqlite==2.0.0
apache-airflow-providers-ssh==2.1.0

### Deployment

Official Apache Airflow Helm Chart

### Deployment details

Official Helm Chart on GKE using CeleryKubernetesExecutor.

### What happened

I'm unable to Run Tasks from the UI when using CeleryKubernetesExecutor. It just shows the error "Only works with the Celery or Kubernetes executors, sorry". 
<img width="1792" alt="Captura de Pantalla 2021-09-22 a la(s) 17 00 30" src="https://user-images.githubusercontent.com/2586758/134413668-5b638941-bb50-44ff-9349-d53326d1f489.png">




### What you expected to happen

It should be able to run Tasks from the UI when using CeleryKubernetesExecutor, as it only is a "selective superset" (based on queue) of both the Celery and Kubernetes executors.

### How to reproduce

1. Run an Airflow instance with the CeleryKubernetes executor.
2. Go to any DAG
3. Select a Task
4. Press the "Run" button.
5. Check the error.

### Anything else

I will append an example PR as a comment.

### Are you willing to submit PR?

- [x] Yes I am willing to submit a PR!

### Code of Conduct

- [X] I agree to follow this project's [Code of Conduct](https://github.com/apache/airflow/blob/main/CODE_OF_CONDUCT.md)

airflow/www/views.py
"""Pre update hook."""
        item.execution_date = timezone.make_aware(item.execution_date)
        item.value = XCom.serialize_value(item.value)
def lazy_add_provider_discovered_options_to_connection_form():
    """Adds provider-discovered connection parameters as late as possible"""
    def _get_connection_types() -> List[Tuple[str, str]]:
        """Returns connection types available."""
        _connection_types = [
            ('fs', 'File (path)'),
            ('mesos_framework-id', 'Mesos Framework ID'),
            ('email', 'Email'),
        ]
        providers_manager = ProvidersManager()
        for connection_type, provider_info in providers_manager.hooks.items():
            if provider_info:
                _connection_types.append((connection_type, provider_info.hook_name))
        return _connection_types
    ConnectionForm.conn_type = SelectField(
        lazy_gettext('Connection Type'),
        choices=sorted(_get_connection_types(), key=itemgetter(1)),
        widget=Select2Widget(),
        validators=[InputRequired()],
        description="""
            Connection Type missing?
            Make sure you've installed the corresponding Airflow Provider Package.
        """,
    )
    for key, value in ProvidersManager().connection_form_widgets.items():
        setattr(ConnectionForm, key, value.field)
class ConnectionFormWidget(FormWidget):