Describe the meaning of each setting in pg_settings

[neverchanje]

          I agree that we need descriptions somewhere for these settings. But in order to reduce our efforts, I suggest documenting them through `pg_settings` https://www.postgresql.org/docs/current/view-pg-settings.html, which is the system table for all settings. @yezizp2012 There is a column named 'short_desc' that will provide users their meaning.

https://crate.io/docs/crate/reference/en/5.3/config/session.html CrateDB indeeds maintain a doc. But not all databases did the same.

Originally posted by @neverchanje in https://github.com/risingwavelabs/risingwave-docs/issues/1058#issuecomment-1639726394

[neverchanje]

Please feel free to reassign this issue to someone else. It's not urgent.

[github-actions]

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[yezizp2012]

Completed by #15108 .