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**Description**

I want to specify the cipher to use when creating a SftpHook. Currently this is not possible because there is not a way to propagate the value to CnOpts. 

https://github.com/apache/airflow/blob/master/airflow/providers/sftp/hooks/sftp.py
https://pysftp.readthedocs.io/en/release_0.2.9/pysftp.html?#pysftp.CnOpts
https://pysftp.readthedocs.io/en/release_0.2.9/cookbook.html

**Use case / motivation**

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I want to be able to access SFTP servers that have disabled access from connection with weak ciphers.

airflow/providers/sftp/hooks/sftp.py
#
#
#
"""This module contains SFTP hook."""
import datetime
import stat
from typing import Dict, List, Optional, Tuple
import pysftp
from airflow.providers.ssh.hooks.ssh import SSHHook
class SFTPHook(SSHHook):
    """
    This hook is inherited from SSH hook. Please refer to SSH hook for the input
    arguments.
    Interact with SFTP. Aims to be interchangeable with FTPHook.
    :Pitfalls::
        - In contrast with FTPHook describe_directory only returns size, type and
          modify. It doesn't return unix.owner, unix.mode, perm, unix.group and
          unique.
        - retrieve_file and store_file only take a local full path and not a
           buffer.
        - If no mode is passed to create_directory it will be created with 777
          permissions.
    Errors that may occur throughout but should be handled downstream.
    """
    def __init__(self, ftp_conn_id: str = 'sftp_default', *args, **kwargs) -> None: