### 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
"""Shows landing times."""
        default_dag_run = conf.getint('webserver', 'default_dag_run_display_number')
        dag_id = request.args.get('dag_id')
        dag: DAG = current_app.dag_bag.get_dag(dag_id)
        dag_model = DagModel.get_dagmodel(dag_id)
        base_date = request.args.get('base_date')
        num_runs = request.args.get('num_runs', default=default_dag_run, type=int)
        if base_date:
            base_date = timezone.parse(base_date)
        else:
            base_date = dag.get_latest_execution_date() or timezone.utcnow()
        wwwutils.check_import_errors(dag.fileloc, session)
        root = request.args.get('root')
        if root:
            dag = dag.partial_subset(task_ids_or_regex=root, include_upstream=True, include_downstream=False)
        tis = dag.get_task_instances_before(base_date, num_runs, session=session)
        chart_height = wwwutils.get_chart_height(dag)
        chart = nvd3.lineChart(
            name="lineChart", x_is_date=True, height=chart_height, chart_attr=self.line_chart_attr
        )
        y_points = {}
        x_points = {}
        for task in dag.tasks:
            task_id = task.task_id
            y_points[task_id] = []
            x_points[task_id] = []
            for ti in tis:
                ts = dag.get_run_data_interval(ti.dag_run).end