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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
"""
        Returns True if a remote entity exists
        :param path: full path to the remote file or directory
        :type path: str
        """
        conn = self.get_conn()
        return conn.exists(path)
    @staticmethod
    def _is_path_match(path: str, prefix: Optional[str] = None, delimiter: Optional[str] = None) -> bool:
        """
        Return True if given path starts with prefix (if set) and ends with delimiter (if set).
        :param path: path to be checked
        :type path: str
        :param prefix: if set path will be checked is starting with prefix
        :type prefix: str
        :param delimiter: if set path will be checked is ending with suffix
        :type delimiter: str
        :return: bool
        """
        if prefix is not None and not path.startswith(prefix):
            return False
        if delimiter is not None and not path.endswith(delimiter):