docs: Improved image dataset creation sample

[kweinmeister]

• Includes imports within code sample
• Provides example of src_uris parameter

[snippet-bot]

Here is the summary of changes.

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• samples/model-builder/create_and_import_dataset_image_sample.py:16, tag aiplatform_sdk_create_and_import_dataset_image_sample

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• samples/model-builder/create_and_import_dataset_image_sample.py:20, tag aiplatform_sdk_create_and_import_dataset_image_sample

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[nicain]

LGTM