### 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
"""Process form data."""
        conn_type = form.data['conn_type']
        conn_id = form.data["conn_id"]
        extra = {
            key: form.data[key]
            for key in self.extra_fields
            if key in form.data and key.startswith(f"extra__{conn_type}__")
        }
        
        
        extra_conn_params = form.data.get("extra")
        if extra_conn_params:
            try:
                extra.update(json.loads(extra_conn_params))
            except (JSONDecodeError, TypeError):
                flash(
                    Markup(
                        "<p>The <em>Extra</em> connection field contained an invalid value for Conn ID: "
                        f"<q>{conn_id}</q>.</p>"
                        "<p>If connection parameters need to be added to <em>Extra</em>, "
                        "please make sure they are in the form of a single, valid JSON object.</p><br>"
                        "The following <em>Extra</em> parameters were <b>not</b> added to the connection:<br>"
                        f"{extra_conn_params}",
                    ),
                    category="error",
                )
        if extra.keys():
            form.extra.data = json.dumps(extra)
    def prefill_form(self, form, pk):