### 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
dagtags = session.query(DagTag.name).distinct(DagTag.name).all()
            tags = [
                {"name": name, "selected": bool(arg_tags_filter and name in arg_tags_filter)}
                for name, in dagtags
            ]
            import_errors = session.query(errors.ImportError).order_by(errors.ImportError.id)
            if (permissions.ACTION_CAN_READ, permissions.RESOURCE_DAG) not in user_permissions:
                
                import_errors = import_errors.join(
                    DagModel, DagModel.fileloc == errors.ImportError.filename
                ).filter(DagModel.dag_id.in_(filter_dag_ids))
            for import_error in import_errors:
                flash(
                    "Broken DAG: [{ie.filename}] {ie.stacktrace}".format(ie=import_error),
                    "dag_import_error",
                )
        from airflow.plugins_manager import import_errors as plugin_import_errors
        for filename, stacktrace in plugin_import_errors.items():
            flash(
                f"Broken plugin: [{filename}] {stacktrace}",
                "error",
            )
        num_of_pages = int(math.ceil(num_of_all_dags / float(dags_per_page)))
        state_color_mapping = State.state_color.copy()
        state_color_mapping["null"] = state_color_mapping.pop(None)
        page_title = conf.get(section="webserver", key="instance_name", fallback="DAGs")
        dashboard_alerts = [
            fm for fm in settings.DASHBOARD_UIALERTS if fm.should_show(current_app.appbuilder.sm)
        ]
        def _iter_parsed_moved_data_table_names():