### 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
.group_by(_convert_to_date(session, DagRun.execution_date), DagRun.state)
            .order_by(_convert_to_date(session, DagRun.execution_date).asc())
            .all()
        )
        dag_states = [
            {
                
                
                'date': dr.date if isinstance(dr.date, str) else dr.date.isoformat(),
                'state': dr.state,
                'count': dr.count,
            }
            for dr in dag_states
        ]
        data = {
            'dag_states': dag_states,
            'start_date': (dag.start_date or DateTime.utcnow()).date().isoformat(),
            'end_date': (dag.end_date or DateTime.utcnow()).date().isoformat(),
        }
        doc_md = wwwutils.wrapped_markdown(getattr(dag, 'doc_md', None))
        
        data = htmlsafe_json_dumps(data, separators=(',', ':'))
        return self.render_template(
            'airflow/calendar.html',
            dag=dag,
            doc_md=doc_md,
            data=data,
            root=root,
            dag_model=dag_model,
        )