### 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
DateTimeWithNumRunsWithDagRunsForm,
    TaskInstanceEditForm,
)
from airflow.www.widgets import AirflowModelListWidget
PAGE_SIZE = conf.getint('webserver', 'page_size')
FILTER_TAGS_COOKIE = 'tags_filter'
FILTER_STATUS_COOKIE = 'dag_status_filter'
def truncate_task_duration(task_duration):
    """
    Cast the task_duration to an int was for optimization for large/huge dags if task_duration > 10s
    otherwise we keep it as a float with 3dp
    """
    return int(task_duration) if task_duration > 10.0 else round(task_duration, 3)
def get_safe_url(url):
    """Given a user-supplied URL, ensure it points to our web server"""
    valid_schemes = ['http', 'https', '']
    valid_netlocs = [request.host, '']
    if not url:
        return url_for('Airflow.index')
    parsed = urlparse(url)
    
    
    if ';' in unquote(url):
        return url_for('Airflow.index')
    query = parse_qsl(parsed.query, keep_blank_values=True)
    url = parsed._replace(query=urlencode(query)).geturl()
    if parsed.scheme in valid_schemes and parsed.netloc in valid_netlocs:
        return url
    return url_for('Airflow.index')
def get_date_time_num_runs_dag_runs_form_data(www_request, session, dag):