disabled Ssh algorithms

[thorinaboenke]

Problem

Connecting to legacy SSH servers (for example e.g. OpenSSH 4.7 on Metasploitable2, important for training puposes) with
key-based auth fails because paramiko negotiates rsa-sha2-256/rsa-sha2-512 by default, which old servers don't support.

Changes

• schemas/ssh.py: added disabled_algorithms: Optional[Dict[str, List[str]]] = None
• executors/ssh/sshexecutor.py: initialized self.disabled_algorithms = None in set_defaults(), cache it in cache_settings(), and pass it to connect() calls
• updated docs

Usage

  - type: ssh
    hostname: $TARGET
    username: root
    key_filename: /tmp/backdoor_key
    disabled_algorithms:
      pubkeys:
        - rsa-sha2-256
        - rsa-sha2-512