### 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
}
        )
        doc_md = wwwutils.wrapped_markdown(getattr(dag, 'doc_md', None))
        task_log_reader = TaskLogReader()
        if task_log_reader.supports_external_link:
            external_log_name = task_log_reader.log_handler.log_name
        else:
            external_log_name = None
        data = self._get_tree_data(dag_runs, dag, base_date, session=session)
        
        data = htmlsafe_json_dumps(data, separators=(',', ':'))
        return self.render_template(
            'airflow/tree.html',
            operators=sorted({op.task_type: op for op in dag.tasks}.values(), key=lambda x: x.task_type),
            root=root,
            form=form,
            dag=dag,
            doc_md=doc_md,
            data=data,
            num_runs=num_runs,
            show_external_log_redirect=task_log_reader.supports_external_link,
            external_log_name=external_log_name,
            dag_model=dag_model,
            auto_refresh_interval=conf.getint('webserver', 'auto_refresh_interval'),
        )
    @expose('/calendar')
    @auth.has_access(
        [
            (permissions.ACTION_CAN_READ, permissions.RESOURCE_DAG),
            (permissions.ACTION_CAN_READ, permissions.RESOURCE_TASK_INSTANCE),