Resolve "Implement new RegisterWorkflow with SSH Password"

Closes #203 (closed)

This is one of the bigger and older changes we had laying around. I hope that I got all the correct commits and lines of code. And that this isn't too RWTH-specific?

This was implemented before the project refactoring, so I am not sure if the classes are even inside the correct modules.
Similar to the LdapWorker we tried to implement a more generic SshWorker and Connector.

Via the service properties we can configure ssh_key_filepath, ssh_known_hosts, ssh_host, ssh_user, ssh_key_password and the ssh_input_template.
This way we connect to the hpc system with a specific user that can only set passwords. And pass the data as a json object (defined via the template) to STDIN. Which then gets processed by a script, but that already is on the side of hpc.