feat(catalog): support DBeaver constraints view

[fuyufjh]

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What's changed and what's your intention?

Implemented pg_catalog.pg_constraint. Only primary keys are listed because this is the only constraints supported in RisingWave.

closes #15197
closes #15205

Checklist

• I have written necessary rustdoc comments
• I have added necessary unit tests and integration tests
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Documentation

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Release note

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• Support pg_catalog.pg_constraint for DBeaver compatibility.

[yezizp2012]

LGTM, generation_expression and is_generated has been added in rw_columns, you may need to resolve the conflict.

[fuyufjh]

Just restructured code to reduce indent.