### 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
"""Pool link rendering."""
        pool_id = self.get('pool')
        if pool_id is not None:
            url = url_for('TaskInstanceModelView.list', _flt_3_pool=pool_id)
            return Markup("<a href='{url}'>{pool_id}</a>").format(url=url, pool_id=pool_id)
        else:
            return Markup('<span class="label label-danger">Invalid</span>')
    def frunning_slots(self):
        """Running slots rendering."""
        pool_id = self.get('pool')
        running_slots = self.get('running_slots')
        if pool_id is not None and running_slots is not None:
            url = url_for('TaskInstanceModelView.list', _flt_3_pool=pool_id, _flt_3_state='running')
            return Markup("<a href='{url}'>{running_slots}</a>").format(url=url, running_slots=running_slots)
        else:
            return Markup('<span class="label label-danger">Invalid</span>')
    def fqueued_slots(self):
        """Queued slots rendering."""
        pool_id = self.get('pool')
        queued_slots = self.get('queued_slots')
        if pool_id is not None and queued_slots is not None:
            url = url_for('TaskInstanceModelView.list', _flt_3_pool=pool_id, _flt_3_state='queued')
            return Markup("<a href='{url}'>{queued_slots}</a>").format(url=url, queued_slots=queued_slots)
        else:
            return Markup('<span class="label label-danger">Invalid</span>')
    formatters_columns = {'pool': pool_link, 'running_slots': frunning_slots, 'queued_slots': fqueued_slots}
    validators_columns = {'pool': [validators.DataRequired()], 'slots': [validators.NumberRange(min=-1)]}
def _can_create_variable() -> bool:
    return current_app.appbuilder.sm.has_access(permissions.ACTION_CAN_CREATE, permissions.RESOURCE_VARIABLE)
class VariableModelView(AirflowModelView):