### 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)

airflow/www/views.py
'url': None,
                    'error': f"can't find dag {dag} or task_id {task_id}",
                }
            )
            response.status_code = 404
            return response
        task = dag.get_task(task_id)
        try:
            url = task.get_extra_links(dttm, link_name)
        except ValueError as err:
            response = jsonify({'url': None, 'error': str(err)})
            response.status_code = 404
            return response
        if url:
            response = jsonify({'error': None, 'url': url})
            response.status_code = 200
            return response
        else:
            response = jsonify({'url': None, 'error': f'No URL found for {link_name}'})
            response.status_code = 404
            return response
    @expose('/object/task_instances')
    @auth.has_access(
        [
            (permissions.ACTION_CAN_READ, permissions.RESOURCE_DAG),
            (permissions.ACTION_CAN_READ, permissions.RESOURCE_TASK_INSTANCE),
        ]
    )
    @action_logging
    def task_instances(self):