feat: Option to add model signature

[JonasGoebel]

What does the PR do?

This pull requests adds a signature option to log_model and save_model. Using this option, a MLflow signature can be added when uploading the model to the MLflow registry.
The parameter default is None so that the methods still work when no signature is given.

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• build
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Related PRs:

Where should the reviewer start?

deploy/mlflow-triton-plugin/scripts/triton_flavor.py

Test plan:

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Background

I want to use the MLflow Model input and output visualisation together with the triton flavor.

Related Issues: (use one of the action keywords Closes / Fixes / Resolves / Relates to)