### 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
}
    @action(
        'clear',
        lazy_gettext('Clear'),
        lazy_gettext(
            'Are you sure you want to clear the state of the selected task'
            ' instance(s) and set their dagruns to the QUEUED state?'
        ),
        single=False,
    )
    @action_has_dag_edit_access
    @provide_session
    def action_clear(self, task_instances, session=None):
        """Clears the action."""
        try:
            dag_to_tis = collections.defaultdict(list)
            for ti in task_instances:
                dag = current_app.dag_bag.get_dag(ti.dag_id)
                dag_to_tis[dag].append(ti)
            for dag, task_instances_list in dag_to_tis.items():
                models.clear_task_instances(task_instances_list, session, dag=dag)
            session.commit()
            flash(f"{len(task_instances)} task instances have been cleared")
        except Exception as e:
            flash(f'Failed to clear task instances: "{e}"', 'error')
        self.update_redirect()
        return redirect(self.get_redirect())
    @action('muldelete', 'Delete', "Are you sure you want to delete selected records?", single=False)
    @action_has_dag_edit_access
    def action_muldelete(self, items):