Make sure node parameters can be iterables or Parameter when creating spatial nodes

[stinebuu]

This fixes #2251

[med-ayssar]

Thank you @stinebuu, it works pretty well. However, I would like addressing another issues regarding the positions parameter.
Once the positions are given to the create function, we will have the following NodeCollection instance: x = NodeCollection(metadata=spatial, model=iaf_psc_alpha, size=6, first=19, last=24), but calling y = ǹest.NodeCollection(x.tolist()) return another NodeCollection instance with the metatdata set to None, y = NodeCollection(metadata=None, model=iaf_psc_alpha, size=6, first=19, last=24), and I think that the instance y must also somehow have its metadata equal to the metadata of x, as they both point to the same collection.

[stinebuu]

Thanks @med-ayssar. Could you create another issue about this? I do not think this should be solved in this PR as it is a separate issue. The problem is a bit more complex for this second issue, I am not sure there is an easy fix, we would need to look into it. The metadata needs to be set on Kernel level, and we would need to find a way to check if the node ids have metadata. It would be great if you could say a little about when you would need this in the issue as well. We are aware of the issue already, and would be happy to look into it if there is a real use case, but up to now there hasn't really been any use cases.

[hakonsbm]

Thanks!