Add support for sending suffixes in BatchRequestCompletionsVertex

What does this merge request do and why?

Adds the option to include suffixes when calling vertex.

1. Adds a --include-suffix parameter defaulted to False

How to set up and validate locally

1. Running the pipeline with suffix

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.2023-10-04_bcardoso_t1_suffix \
    --throttle_sec 0.01 \
    --num_samples_per_file 5 \
    --language python \
    --include-suffix

Merge request checklist

• Tests added for new functionality. If not, please raise an issue to follow up.
• Documentation added/updated, if needed.