add Text Generation udf that accepts spans

[MarleneKress79789]

Summary

We will use the transformer-extension for Named Entity Recognition, Topic Classification and Sentiment Classification in ExasolAI. We will store the documents and their parts as spans. To be able to join back the annotations produced by the transformer-extensions to the documents and their parts, we need input and output spans into/from the Prediction UDFs.

Text Generation(input span = output span)

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1. add spans as optional input to TextGeneration UDF
2. add spans as output to TextGeneration UDF
3. add additional udf call for TextGeneration with spans, which only gets installed if feature flag is set during udf-installation
4. find model for TextGeneration which works with spans
5. add tests for TextGeneration utilising spans