### 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
"""Set state to failed."""
        try:
            count = 0
            altered_tis = []
            for dr in session.query(DagRun).filter(DagRun.id.in_([dagrun.id for dagrun in drs])).all():
                count += 1
                altered_tis += set_dag_run_state_to_failed(
                    current_app.dag_bag.get_dag(dr.dag_id), dr.execution_date, commit=True, session=session
                )
            altered_ti_count = len(altered_tis)
            flash(
                "{count} dag runs and {altered_ti_count} task instances "
                "were set to failed".format(count=count, altered_ti_count=altered_ti_count)
            )
        except Exception:
            flash('Failed to set state', 'error')
        return redirect(self.get_default_url())
    @action(
        'set_success',
        "Set state to 'success'",
        "All task instances would also be marked as success, are you sure?",
        single=False,
    )
    @action_has_dag_edit_access
    @provide_session
    def action_set_success(self, drs, session=None):