Move conda_env and model_namearguments from MlflowPipelineHook to PipelineML class

[Galileo-Galilei]

As discussed in #29:

• this is necessary for plugin auto registration because auto-registered hooks must not have arguments
• this enable to register several PipelineML object inside the same project, which is a realistic scenario w want to support
• this makes more sense because these arguments only affects PipelineML objects and not all the scope of the hook.