Support adding multiple weights using build_model

[oeway]

Support adding multiple weights using build_model

[ivan-ea]

Thanks @constantinpape the add_weights function seems exactly what I was missing.
I was following the model creation notebook, since I need to get the
deepimagej_config too. Maybe I could add the add_weights to the example notebook
once I figure out how to use it.

[ivan-ea]

For context:
I was not sure if it was possible to generate models with multiple weight files with the build_model function.
Also I wondered if I missed something, since the website has the option to choose between several weight formats to download.

Some models have 2 weights in the rdf (for example impartial-shrimp), so I was curious how they might have built them.

[constantinpape]

Adding multiple weights is supported, but not directly via the build_model function.
Instead, you would need to use add_weights. (As a side note: we should add this to the model creation notebook).

I think having the option to do this directly in build_model would be nice, but I don't have capacity to implement this at this points; but I would be happy to review a PR if someone wants to give it a try.

[constantinpape]

Maybe I could add the add_weights to the example notebook
once I figure out how to use it.

That would be great!