### 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)

tests/www/views/test_views_connection.py
description='MongoDB2',
        host='localhost',
        schema='airflow',
        port=3306,
    )
    conn3 = Connection(
        conn_id='test_duplicate_postgres_connection_copy1',
        conn_type='FTP',
        description='Postgres',
        host='localhost',
        schema='airflow',
        port=3306,
    )
    with create_session() as session:
        session.query(Connection).delete()
        session.add_all([conn1, conn2, conn3])
        session.commit()
    data = {"action": "mulduplicate", "rowid": [conn1.id, conn3.id]}
    resp = admin_client.post('/connection/action_post', data=data, follow_redirects=True)
    expected_result = {
        'test_duplicate_gcp_connection',
        'test_duplicate_gcp_connection_copy1',
        'test_duplicate_mysql_connection',
        'test_duplicate_postgres_connection_copy1',
        'test_duplicate_postgres_connection_copy2',
    }
    response = {conn[0] for conn in session.query(Connection.conn_id).all()}
    assert resp.status_code == 200
    assert expected_result == response