Add function_version to Call

[Pryz]

This changes add a function_version field to the Call data model to allow selecting the right version of the code during execution.

[achille-roussel]

I guess the only question would be whether this field is better named function_version or version, function/function_version is a bit redundant, but also very clear.

I don't have a strong opinion on the matter, just bringing it up in case it inspires a change.

[Pryz]

Yes, I was considering just using version at first but might be better to be very clear here. Otherwise it could be a function version, endpoint version, input data model version, etc

Switching to version since it indicates the version of the code to be execution and not the version of a single function within that code.