**Description** 

Since sensitive informations in the connection object (specifically the extras field) are now being masked based on sensitive key names, we should consider adding some common sensitive key names.

`private_key` from [ssh connection](https://airflow.apache.org/docs/apache-airflow-providers-ssh/stable/connections/ssh.html) is an examples.

**Use case / motivation**

Extras field used to be blocked out entirely before the sensitive value masking feature (#15599).

[Before in 2.0.2](https://github.com/apache/airflow/blob/2.0.2/airflow/hooks/base.py#L78
) and [after in 2.1.0](https://github.com/apache/airflow/blob/2.1.0/airflow/hooks/base.py#L78
).

Extras field containing sensitive information now shown unless the key contains sensitive names.

**Are you willing to submit a PR?** 

@ashb has expressed interest in adding this.

airflow/utils/log/secrets_masker.py
if self.ALREADY_FILTERED_FLAG in record.__dict__:
            
            
            return True
        if self.replacer:
            for k, v in record.__dict__.items():
                if k in self._record_attrs_to_ignore:
                    continue
                record.__dict__[k] = self.redact(v)
            if record.exc_info and record.exc_info[1] is not None:
                exc = record.exc_info[1]
                
                exc.args = (self.redact(v) for v in exc.args)
        record.__dict__[self.ALREADY_FILTERED_FLAG] = True
        return True
    def _redact_all(self, item: "RedactableItem") -> "RedactableItem":
        if isinstance(item, dict):
            return {dict_key: self._redact_all(subval) for dict_key, subval in item.items()}
        elif isinstance(item, str):
            return '***'
        elif isinstance(item, (tuple, set)):
            
            return tuple(self._redact_all(subval) for subval in item)
        elif isinstance(item, Iterable):
            return list(self._redact_all(subval) for subval in item)
        else:
            return item
    
    def redact(self, item: "RedactableItem", name: str = None) -> "RedactableItem":