### Apache Airflow version

2.1.3 (latest released)

### Operating System

Debian Buster

### Versions of Apache Airflow Providers

_No response_

### Deployment

Managed Services (Astronomer, Composer, MWAA etc.)

### Deployment details

Running `quay.io/astronomer/ap-airflow:2.1.3-buster` Docker image

### What happened

In the task attributes view of a BashOperator, the `template_ext` row doesn't show any value, while I would expect to see `('.sh', '.bash')`.

![image](https://user-images.githubusercontent.com/6249654/131467817-8620f68d-0f3d-491d-ad38-cbf5b91cdcb3.png)


### What you expected to happen

Expect to see correct `template_ext` value

### How to reproduce

Run a BashOperator and browse to Instance Details --> scroll down to `template_ext` row

### Anything else

Spent a little time trying to figure out what could be the reason, but haven't found the problem yet. Therefore created issue to track.

### 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/models/baseoperator.py
"""Abstract base class that defines how we get an operator link."""
    operators: ClassVar[List[Type[BaseOperator]]] = []
    """
    This property will be used by Airflow Plugins to find the Operators to which you want
    to assign this Operator Link
    :return: List of Operator classes used by task for which you want to create extra link
    """
    @property
    @abstractmethod
    def name(self) -> str:
        """
        Name of the link. This will be the button name on the task UI.
        :return: link name
        """
    @abstractmethod
    def get_link(self, operator: BaseOperator, dttm: datetime) -> str:
        """
        Link to external system.
        :param operator: airflow operator
        :param dttm: datetime
        :return: link to external system
        """