### 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
ignore_ti_state=ignore_ti_state,
        )
        failed_deps = list(ti.get_failed_dep_statuses(dep_context=dep_context))
        if failed_deps:
            failed_deps_str = ", ".join(f"{dep.dep_name}: {dep.reason}" for dep in failed_deps)
            flash(
                "Could not queue task instance for execution, dependencies not met: "
                "{}".format(failed_deps_str),
                "error",
            )
            return redirect(origin)
        executor.job_id = "manual"
        executor.start()
        executor.queue_task_instance(
            ti,
            ignore_all_deps=ignore_all_deps,
            ignore_task_deps=ignore_task_deps,
            ignore_ti_state=ignore_ti_state,
        )
        executor.heartbeat()
        flash(f"Sent {ti} to the message queue, it should start any moment now.")
        return redirect(origin)
    @expose('/delete', methods=['POST'])
    @auth.has_access(
        [
            (permissions.ACTION_CAN_DELETE, permissions.RESOURCE_DAG),
        ]
    )
    @action_logging
    def delete(self):