feat: adding support and samples for jsonb

[asthamohta]

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[snippet-bot]

Here is the summary of changes.

You are about to add 3 region tags.

• samples/samples/pg_snippets.py:1346, tag spanner_postgresql_jsonb_add_column
• samples/samples/pg_snippets.py:1387, tag spanner_postgresql_jsonb_update_data
• samples/samples/pg_snippets.py:1445, tag spanner_postgresql_jsonb_query_parameter

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