feat: New text Generation Samples

[Thoughtseize1]

I noticed that some samples were missing from our repository. This PR addresses this by adding 2 new samples (listed below) and introducing an extendable test structure.

File	Documentation Link	Region_tag
batch_code_predict.py	Get batch code predictions	aiplatform_batch_code_predict
batch_text_predict.py	Get batch text generations	aiplatform_batch_text_predict

For proper testing, please upload the 2 files to the test environment of the test project with the .JSNOL extension and provide the paths to the model prompts in the format gs://[cloud-samples-data]/[PATH_TO_FILE].jsonl

.json example for batch_code_predict.py. Possible name: prompt_for_batch_code_predict.jsonl

{"prefix":"Write a Python function that determines if a year is a leap year:"}
{"prefix":"Write a unit test for Python code that reverses a string:"}

.json example for batch_text_predict.py. Possible name:prompt_for_batch_text_predict.jsonl

{"prompt":"Give a short description of a machine learning model:"}
{"prompt":"Best recipe for banana bread:"}

Description

Fixes #

Note: Before submitting a pull request, please open an issue for discussion if you are not associated with Google.

Checklist

• [x] I have followed Sample Guidelines from AUTHORING_GUIDE.MD
• [ ] README is updated to include all relevant information
• [x] Tests pass: nox -s py-3.9 (see Test Environment Setup)
• [x] Lint pass: nox -s lint (see Test Environment Setup)
• [ ] These samples need a new API enabled in testing projects to pass (let us know which ones)
• [ ] These samples need a new/updated env vars in testing projects set to pass (let us know which ones)
• [ ] This sample adds a new sample directory, and I updated the CODEOWNERS file with the codeowners for this sample
• [ ] This sample adds a new Product API, and I updated the Blunderbuss issue/PR auto-assigner with the codeowners for this sample
• [ ] Please merge this PR for me once it is approved

[snippet-bot[bot]]

Here is the summary of changes.

You are about to add 2 region tags.

- [generative_ai/batch_predict/batch_code_predict.py:31](https://github.com/GoogleCloudPlatform/python-docs-samples/blob/c40a84844b09e9a9c662a4db668a8643a97e6d2b/generative_ai/batch_predict/batch_code_predict.py#L31), tag `aiplatform_batch_code_predict` - [generative_ai/batch_predict/batch_text_predict.py:31](https://github.com/GoogleCloudPlatform/python-docs-samples/blob/c40a84844b09e9a9c662a4db668a8643a97e6d2b/generative_ai/batch_predict/batch_text_predict.py#L31), tag `aiplatform_batch_text_predict`

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[m-strzelczyk]

I made the following:

• gs://cloud-samples-data/batch/prompt_for_batch_code_predict.jsonl
• gs://cloud-samples-data/batch/prompt_for_batch_text_predict.jsonl