feat: Add initial Model Builder SDK samples

[vinnysenthil]

Adds an initial set of Model Builder SDK samples and their tests, along with a conftest.py file to hold mocks.

Here are the samples added:

• init_sample
• create_and_import_dataset_image_sample
• create_batch_prediction_job_sample
• create_training_pipeline_image_classification_sample

[snippet-bot]

Here is the summary of changes.

You are about to add 4 region tags.

• samples/model-builder/create_and_import_dataset_image_sample.py:19, tag aiplatform_sdk_create_and_import_dataset_image_sample
• samples/model-builder/create_batch_prediction_job_sample.py:19, tag aiplatform_sdk_create_batch_prediction_job_sample
• samples/model-builder/create_training_pipeline_image_classification_sample.py:17, tag aiplatform_sdk_create_training_pipeline_image_classification_sample
• samples/model-builder/init_sample.py:20, tag aiplatform_sdk_init_sample

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[sasha-gitg]

LGTM! Added some comments.

[sasha-gitg]

This seems either superfluous or possibly will cause an error because we would call run on None.

[vinnysenthil]

Not returning None when patching the __init__ caused the following exception:

TypeError: __init__() should return None, not 'MagicMock'

The downstream calls would also be patched so it shouldn't cause an error. Is this alright or should we look for alternative approaches?

[sasha-gitg]

Ah, right. I was wrong on that. Leave it as is. That makes sense, __new__ returns the instance, not __init__.

[vinnysenthil]

PTAL when you get a chance @busunkim96 @tmatsuo — thanks!

[busunkim96]

I recommend turning on Autospeccing (https://docs.python.org/3/library/unittest.mock.html#autospeccing) where possible. It makes it easier to catch incorrect method calls.

The conftest.py approach seems good for sharing code needed by the tests. For very simple mocks IMO it is easier for folks to follow when the mock is right next to the test using the patch() decorator syntax. (example in google-auth)