docs(samples): add region tags

[Sita04]

Add region tags for 2 existing snippets

[snippet-bot]

Here is the summary of changes.

You are about to add 2 region tags.

• samples/hello/main.py:95, tag bigtable_hw_get_by_key
• samples/hello/main.py:106, tag bigtable_hw_scan_all

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