**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 sensitive information from logs"""
import collections
import io
import logging
import re
from typing import TYPE_CHECKING, Iterable, Optional, Set, TypeVar, Union
from airflow.compat.functools import cache, cached_property
if TYPE_CHECKING:
    from airflow.typing_compat import RePatternType
    RedactableItem = TypeVar('RedactableItem')
log = logging.getLogger(__name__)
DEFAULT_SENSITIVE_FIELDS = frozenset(
    {
        'password',
        'secret',
        'passwd',
        'authorization',
        'api_key',
        'apikey',
        'access_token',
    }
)
"""Names of fields (Connection extra, Variable key name etc.) that are deemed sensitive"""
@cache
def get_sensitive_variables_fields():