Enable ssh-dss algorighthm through system variable

We need to connect many SFTP servers and some SFTP servers are still using ` ssh-dss` algorithm for SFTP connection.

We have to use MuleSoft SFTP connector which internally uses `sshd-core-2.12.1` library, by default ` ssh-dss` algorithm are disabled because it is too weak to considered.

I'm able to communicate with these ssh-dss enabled SFTP servers using the settings below. However, I'm unable to apply the same settings in the MuleSoft SFTP connector because we can't modify their library.

```
sshClient.setKeyExchangeFactories(NamedFactory.setUpTransformedFactories(false,
BuiltinDHFactories.VALUES, ClientBuilder.DH2KEX));
sshClient.setSignatureFactories(new ArrayList<>(BuiltinSignatures.VALUES));
```

Could someone please advise if there's a method to enable the ssh-dss algorithm via system variable settings? This would allow us to connect to ssh-dss enabled SFTP servers without any code modifications.

Start by reviewing the sshd-core 2.12.1 algorithm configuration and the shown SSH client factory settings, then check how system properties are currently handled. Done should mean a supported system-variable mechanism can enable the requested ssh-dss-related algorithms without modifying connector library code.

Written by the indexing model from the issue text.