### 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
nonlocal node_count
            node_count += 1
            visited.add(task)
            task_id = task.task_id
            node = {
                'name': task.task_id,
                'instances': [encode_ti(task_instances.get((task_id, d))) for d in dates],
                'num_dep': len(task.downstream_list),
                'operator': task.task_type,
                'retries': task.retries,
                'owner': task.owner,
                'ui_color': task.ui_color,
            }
            if task.downstream_list:
                children = [
                    recurse_nodes(t, visited)
                    for t in task.downstream_list
                    if node_count < node_limit or t not in visited
                ]
                
                
                
                if task.task_id not in expanded:
                    children_key = 'children'
                    expanded.add(task.task_id)
                else:
                    children_key = "_children"