### 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
dag_orm = DagModel.get_dagmodel(dag_id, session=session)
            code = DagCode.get_code_by_fileloc(dag_orm.fileloc)
            html_code = Markup(highlight(code, lexers.PythonLexer(), HtmlFormatter(linenos=True)))
        except Exception as e:
            all_errors += (
                "Exception encountered during "
                + f"dag_id retrieval/dag retrieval fallback/code highlighting:\n\n{e}\n"
            )
            html_code = Markup('<p>Failed to load DAG file Code.</p><p>Details: {}</p>').format(
                escape(all_errors)
            )
        wwwutils.check_import_errors(dag_orm.fileloc, session)
        return self.render_template(
            'airflow/dag_code.html',
            html_code=html_code,
            dag=dag_orm,
            dag_model=dag_orm,
            title=dag_id,
            root=request.args.get('root'),
            wrapped=conf.getboolean('webserver', 'default_wrap'),
        )
    @expose('/dag_details')
    @auth.has_access(
        [
            (permissions.ACTION_CAN_READ, permissions.RESOURCE_DAG),
            (permissions.ACTION_CAN_READ, permissions.RESOURCE_DAG_RUN),
        ]
    )
    @provide_session
    def dag_details(self, session=None):