implementation of the build_model function

[adelovelace]

… model from the components

Description

Fix #(issue)

In following the example of how to use ModularTorchModel in the implementation of

modular_model.load_from_pretrained(pretrain_modular_model, components=['linear']) 

there was a failure of the load_from_pretrained function because this use build_model function that builds the model from the entered components and the same was not defined.

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