feat(catalog): implement pg_settings

[wangrunji0408]

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What's changed and what's your intention?

resolve #15105, fix #14012

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[neverchanje]

Thanks! LGTM

[yezizp2012]

LGTM!

[xxchan]

Also resolves #8850? 😄

[BugenZhao]

Also resolves #8850? 😄

Seems not. Another column context and system parameters records are required for that query to work.