change ComposerModel output type

[hyenal]

What does this PR do?

This PR changes the output type of the ComposerModel. As long as the output type is a tensor, a tensor list, a dictionary of tensors or has a method cpu() (to satisfy this, note that if you return a list of non-tensors it will not break the pipeline) we should be able to return any type.

What issue(s) does this change relate to?

No issue has been opened yet.

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cc: @JAEarly

[mvpatel2000]

Agree it should be more arbitrary. Thanks for the PR!