Leverage Chains from LangChain to selectively apply transformations

• Add the --transformation=<name> param to allow selectively applying transformations through the cli.
• Add a transformation step before AnalyseCodeChunk that applies the specified transformations to the prompt.
  • The transformations are applied in the specified order.

Example:

python promptlib/eval_codebase.py \                                    
    --runner DirectRunner \
    --project unreview-poc-390200e5 \
    --region us-central1 \
    --temp_location "gs://unreview-dataflow/tmp/" \
    --save_main_session \
    --input_bq_table unreview-poc-390200e5:gl_gitlab_codebase.content_v1 \
    --output_bq_table unreview-poc-390200e5:gl_gitlab_codebase.2023-08-28_bcardoso_langchain_t1_parameterized_t5 \
    --throttle_sec 0.01 \
    --num_samples_per_file 5 \
    --language python \
    --transformation imports \
    --transformation prompt_with_file_name_and_language

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Closes #33 (closed)