Handle Model metadata merge

[YohannParis]

Right now when a model is updated, apart of some headers information, everything is overwritten.
https://github.com/DARPA-ASKEM/data-service/blob/main/tds/modules/model/controller.py#L244-L261

We are losing metadata information saved previously.

This is a complex issue to handle in relation to stratification, but for the time being, just merging the properties should be a good start. Or better codifying some of them within the AMR specification.