Functionality/Tutorial for changing `ModelMetadata` and `ModelOutput `

[PicoCentauri]

The ModelMetadata and ModelOutputs are both stored a attributes in an AtomisticModel.

Even though already possible changing them is not very smooth and not well documented. We should either provide a library function for an edit and/or give a tutorial how this can be achieved. If we want to provide a function we have to decide on how it should look like. The most simple approach like

def change_metadata(model: AtomisticModel, new_metadata: ModelMetadata):
    ....

def change_metadata(model: AtomisticModel, new_outputs: ModelOutput):
    ....

are maybe not really helpful as these are single line functions...