### 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
current_dags.order_by(DagModel.dag_id)
                .options(joinedload(DagModel.tags))
                .offset(start)
                .limit(dags_per_page)
                .all()
            )
            user_permissions = current_app.appbuilder.sm.get_current_user_permissions()
            all_dags_editable = (permissions.ACTION_CAN_EDIT, permissions.RESOURCE_DAG) in user_permissions
            can_create_dag_run = (
                permissions.ACTION_CAN_CREATE,
                permissions.RESOURCE_DAG_RUN,
            ) in user_permissions
            can_delete_dag = (
                permissions.ACTION_CAN_DELETE,
                permissions.RESOURCE_DAG,
            ) in user_permissions
            for dag in dags:
                if all_dags_editable:
                    dag.can_edit = True
                else:
                    dag_resource_name = permissions.RESOURCE_DAG_PREFIX + dag.dag_id
                    dag.can_edit = (permissions.ACTION_CAN_EDIT, dag_resource_name) in user_permissions
                dag.can_trigger = dag.can_edit and can_create_dag_run
                dag.can_delete = can_delete_dag
            dagtags = session.query(DagTag.name).distinct(DagTag.name).all()
            tags = [
                {"name": name, "selected": bool(arg_tags_filter and name in arg_tags_filter)}
                for name, in dagtags
            ]
            import_errors = session.query(errors.ImportError).order_by(errors.ImportError.id)