docs: add samples using SQL methods via the bigframes.bigquery module

[rey-esp]

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Fixes #<issue_number_goes_here> 🦕

[snippet-bot]

Here is the summary of changes.

You are about to add 2 region tags.

• samples/snippets/bigquery_modules_test.py:17, tag bigquery_dataframes_bigquery_methods_struct
• samples/snippets/bigquery_modules_test.py:39, tag bigquery_dataframes_bigquery_methods_scalar

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