### Apache Airflow version

2.2.0

### Operating System

Debian buster

### Versions of Apache Airflow Providers

_No response_

### Deployment

Astronomer

### Deployment details

astro dev start

### What happened

When I have tried to duplicate a connection first time it has created a connection with hello_copy1 and duplicating the same connection second time giving me an error of 
```Connection hello_copy2 can't be added. Integrity error, probably unique constraint.```




### What you expected to happen

It should create a connection with name hello_copy3 or the error message should be more user friendly.

### How to reproduce

https://github.com/apache/airflow/pull/15574#issuecomment-912438705

### Anything else

Suggested Error 
```
Connection hello_copy2 can't be added because it already exists.
```
or
Change the number logic in _copyN so the new name will be always unique.


### 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)

tests/www/views/test_views_connection.py
init_views.init_connection_form()
    resp = admin_client.post('/connection/add', data=CONNECTION, follow_redirects=True)
    check_content_in_response('Added Row', resp)
def test_prefill_form_null_extra():
    mock_form = mock.Mock()
    mock_form.data = {"conn_id": "test", "extra": None}
    cmv = ConnectionModelView()
    cmv.prefill_form(form=mock_form, pk=1)
def test_process_form_extras():
    """
    Test the handling of connection parameters set with the classic `Extra` field as well as custom fields.
    """
    
    mock_form = mock.Mock()
    mock_form.data = {
        "conn_type": "test",
        "conn_id": "extras_test",
        "extra": '{"param1": "param1_val"}',
        "extra__test__custom_field": "custom_field_val",
    }
    cmv = ConnectionModelView()
    cmv.extra_fields = ["extra__test__custom_field"]  
    cmv.process_form(form=mock_form, is_created=True)
    assert json.loads(mock_form.extra.data) == {
        "extra__test__custom_field": "custom_field_val",
        "param1": "param1_val",
    }