docs(samples): add product import samples

[tetiana-karasova]

Thank you for opening a Pull Request! Before submitting your PR, there are a few things you can do to make sure it goes smoothly:

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Fixes #<issue_number_goes_here> 🦕

[snippet-bot]

Here is the summary of changes.

You are about to add 3 region tags.

• samples/interactive-tutorials/product/import_products_big_query_table.py:15, tag retail_import_products_from_big_query
• samples/interactive-tutorials/product/import_products_gcs.py:15, tag retail_import_products_from_gcs
• samples/interactive-tutorials/product/import_products_inline_source.py:15, tag retail_import_products_from_inline_source

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