Update docs for pg-safeupdate

[encima]

I have read the CONTRIBUTING.md file.

YES

What kind of change does this PR introduce?

Docs update

What is the current behavior?

Current examples in docs are not functional

What is the new behavior?

Update examples for 2 scenarios:

1. Using pg-safeupdate on a per-user basis
2. Using pg-safeupdate on all connections to a database

Add link to resource on using pg-safeupdate with PostgREST

[supabase]

No changes detected in supabase directory.
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Name	Status	Preview	Comments	Updated (UTC)
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