### 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
"""
        A restful endpoint that returns external links for a given Operator
        It queries the operator that sent the request for the links it wishes
        to provide for a given external link name.
        API: GET
        Args: dag_id: The id of the dag containing the task in question
              task_id: The id of the task in question
              execution_date: The date of execution of the task
              link_name: The name of the link reference to find the actual URL for
        Returns:
            200: {url: <url of link>, error: None} - returned when there was no problem
                finding the URL
            404: {url: None, error: <error message>} - returned when the operator does
                not return a URL
        """
        dag_id = request.args.get('dag_id')
        task_id = request.args.get('task_id')
        execution_date = request.args.get('execution_date')
        link_name = request.args.get('link_name')
        dttm = timezone.parse(execution_date)
        dag = current_app.dag_bag.get_dag(dag_id)
        if not dag or task_id not in dag.task_ids:
            response = jsonify(
                {