Merge models from different users

[szmoe]

We need a feature that enables the merging of uploaded models.

For example, ten participants independently built models for the same intervention on their own devices. This results in either 10 full models or 10 partial ones. To create a comprehensive final model, we need to combine all their contributions, ensuring all input nodes from each participant are included.

[szmoe]

Maybe a feature to upload several models to the same page. Then, we can merge (add or delete) input nodes manually.