**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
"""
    Mask a secret from appearing in the task logs.
    If ``name`` is provided, then it will only be masked if the name matches
    one of the configured "sensitive" names.
    If ``secret`` is a dict or a iterable (excluding str) then it will be
    recursively walked and keys with sensitive names will be hidden.
    """
    
    from airflow import settings
    
    
    if not settings.MASK_SECRETS_IN_LOGS or not secret:
        return
    _secrets_masker().add_mask(secret, name)
def redact(value: "RedactableItem", name: str = None) -> "RedactableItem":
    """Redact any secrets found in ``value``."""
    return _secrets_masker().redact(value, name)
@cache
def _secrets_masker() -> "SecretsMasker":
    for flt in logging.getLogger('airflow.task').filters:
        if isinstance(flt, SecretsMasker):
            return flt
    raise RuntimeError("No SecretsMasker found!")
class SecretsMasker(logging.Filter):