Define arguments-variable like the API

[rndmh3ro]

We currently define the the arguments variable takes a dict as an argument: https://github.com/T-Systems-MMS/ansible-collection-icinga-director/blob/a37201aec640f21d0ae33638b121a83f5fc93848/plugins/modules/icinga_command_template.py#L196

Now the actual arguments variable not only takes a dict as input but a string as well. However Ansible provides no native way to say that this variable can be a string or a dict (for me that's rather a problem with the Icinga-API). So we'd need to set the variable to raw and then check if it is actually a dict or string with our own logic.

And even then we probably could not display this correct in the docs since the docs have to match the implementation.