fix: Use dataset_id & table_id as the key of set 'grouped_tables' in bigquery_metadata_extractor

[xuan616]

Fix the issue that some table keys of sharded tables are missing from BQ metadata extractor. Currently, there is a set 'grouped_tables' storing table_prefix of sharded tables to avoid duplicate metadata records, but it is possible the table prefixes would be same in different datasets.

Summary of Changes

Related issue: 833

Sharded tables will use the concatenation of dataset_id & table_id as the key of set 'grouped_tables' in bigquery_metadata_extractor

Tests

No more tests were added and current test can still work

Documentation

More details are in issue 833

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[feng-tao]

@crazy-2020 could you update the DCO?

[xuan616]

@crazy-2020 could you update the DCO?

Sure, updated