### Apache Airflow version

2.2.0 (latest released)

### Operating System

Ubuntu

### Versions of Apache Airflow Providers

_No response_

### Deployment

Other

### Deployment details

Just used `airflow standalone`

### What happened

First:

TaskGroup does not show the tooltip that is defined for that group on hover
![2021-10-19_17h00_18](https://user-images.githubusercontent.com/35238779/137937706-376922b8-2f79-47ac-9789-6007d135f855.png)

Second:

Providing an Operator with `task_group=` instead of TaskGroup as context manager ignores that TaskGroup's default_args. Using the code I provided below, the task "end" in section_3 has the wrong owner.


### What you expected to happen

First:

If a TaskGroup is used and the tooltip is defined like so:
```python
with TaskGroup("section_1", tooltip="Tasks for section_1") as section_1:
```
the information provided with`tooltip="..."` should show on hover, as shown in the official documentation at https://airflow.apache.org/docs/apache-airflow/stable/concepts/dags.html#taskgroups


Second:

Defining a TaskGroup with default_args like
```python
section_3 = TaskGroup("section_3", tooltip="Tasks for section_2", default_args={"owner": "bug"})
```
should result in those default_args being used by tasks defined like so:
```python
end = DummyOperator(task_id="end", task_group=section_3)
```

### How to reproduce

I have tested this with the below code

```python
from datetime import datetime

from airflow.models.dag import DAG
from airflow.operators.bash import BashOperator
from airflow.operators.dummy import DummyOperator
from airflow.utils.task_group import TaskGroup

with DAG(
    dag_id="task_group_test",
    start_date=datetime(2021, 1, 1),
    catchup=False,
    tags=["example"],
    default_args={"owner": "test"},
) as dag:
    start = DummyOperator(task_id="start")

    with TaskGroup("section_1", tooltip="Tasks for section_1") as section_1:
        task_1 = DummyOperator(task_id="task_1")
        task_2 = BashOperator(task_id="task_2", bash_command="echo 1")
        task_3 = DummyOperator(task_id="task_3")

        task_1 >> [task_2, task_3]

    with TaskGroup(
        "section_2", tooltip="Tasks for section_2", default_args={"owner": "overwrite"}
    ) as section_2:
        task_1 = DummyOperator(task_id="task_1")

    section_3 = TaskGroup("section_3", tooltip="Tasks for section_3", default_args={"owner": "bug"})

    end = DummyOperator(task_id="end", task_group=section_3)

    start >> section_1 >> section_2 >> section_3
```

### Anything else

_No response_

### Are you willing to submit PR?

- [ ] 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
"""Shows task instances."""
        dag_id = request.args.get('dag_id')
        dag = current_app.dag_bag.get_dag(dag_id)
        dttm = request.args.get('execution_date')
        if dttm:
            dttm = timezone.parse(dttm)
        else:
            return "Error: Invalid execution_date"
        task_instances = {ti.task_id: alchemy_to_dict(ti) for ti in dag.get_task_instances(dttm, dttm)}
        return json.dumps(task_instances, cls=utils_json.AirflowJsonEncoder)
    @expose('/object/tree_data')
    @auth.has_access(
        [
            (permissions.ACTION_CAN_READ, permissions.RESOURCE_DAG),
            (permissions.ACTION_CAN_READ, permissions.RESOURCE_TASK_INSTANCE),
        ]
    )
    @action_logging
    def tree_data(self):
        """Returns tree data"""
        dag_id = request.args.get('dag_id')
        dag = current_app.dag_bag.get_dag(dag_id)
        if not dag:
            response = jsonify({'error': f"can't find dag {dag_id}"})
            response.status_code = 404
            return response
        root = request.args.get('root')
        if root: