**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
"""Get comma-separated sensitive Variable Fields from airflow.cfg."""
    from airflow.configuration import conf
    sensitive_fields = DEFAULT_SENSITIVE_FIELDS.copy()
    sensitive_variable_fields = conf.get('core', 'sensitive_var_conn_names')
    if sensitive_variable_fields:
        sensitive_fields |= frozenset({field.strip() for field in sensitive_variable_fields.split(',')})
    return sensitive_fields
def should_hide_value_for_key(name):
    """Should the value for this given name (Variable name, or key in conn.extra_dejson) be hidden"""
    from airflow import settings
    if name and settings.HIDE_SENSITIVE_VAR_CONN_FIELDS:
        name = name.strip().lower()
        return any(s in name for s in get_sensitive_variables_fields())
    return False
def mask_secret(secret: Union[str, dict, Iterable], name: str = None) -> None: