### 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
executor = ExecutorLoader.get_default_executor()
        valid_celery_config = False
        valid_kubernetes_config = False
        valid_celery_kubernetes_config = False
        try:
            from airflow.executors.celery_executor import CeleryExecutor
            valid_celery_config = isinstance(executor, CeleryExecutor)
        except ImportError:
            pass
        try:
            from airflow.executors.kubernetes_executor import KubernetesExecutor
            valid_kubernetes_config = isinstance(executor, KubernetesExecutor)
        except ImportError:
            pass
        try:
            from airflow.executors.celery_kubernetes_executor import CeleryKubernetesExecutor
            valid_celery_kubernetes_config = isinstance(executor, CeleryKubernetesExecutor)
        except ImportError:
            pass
        if not valid_celery_config and not valid_kubernetes_config and not valid_celery_kubernetes_config:
            flash("Only works with the Celery, CeleryKubernetes or Kubernetes executors, sorry", "error")
            return redirect(origin)
        dag_run = dag.get_dagrun(execution_date=execution_date)
        ti = dag_run.get_task_instance(task_id=task.task_id)
        ti.refresh_from_task(task)
        
        dep_context = DepContext(
            deps=RUNNING_DEPS,
            ignore_all_deps=ignore_all_deps,
            ignore_task_deps=ignore_task_deps,