dev docs: Update guide with more postgres-metadata info

[def-]

Noticed in #35222 that people are probably not benefiting from those yet.

[github-actions]

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[antiguru]

I'm kinda torn by this one. On the bright side, it makes working with Mz locally faster. On the negative side, it might mean the pain of running in cloud envs isn't visible locally. That said, I don't have a strong take.

[def-]

Same, I'd prefer if we can fix it instead. I guess @aljoscha is working on that right now.