### 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
"""Multiple delete."""
        self.datamodel.delete_all(items)
        self.update_redirect()
        return redirect(self.get_redirect())
    @action(
        'mulduplicate',
        'Duplicate',
        'Are you sure you want to duplicate the selected connections?',
        single=False,
    )
    @provide_session
    @auth.has_access(
        [
            (permissions.ACTION_CAN_CREATE, permissions.RESOURCE_CONNECTION),
            (permissions.ACTION_CAN_READ, permissions.RESOURCE_CONNECTION),
        ]
    )
    def action_mulduplicate(self, connections, session=None):
        """Duplicate Multiple connections"""
        for selected_conn in connections:
            new_conn_id = selected_conn.conn_id