[Backport] fix: accept decomposed DBs in PostgreSQL config validation

Clemens Beckrequested to merge
cb/fix-psql-check-backport into 10-0-stable

What does this MR do?

Backport !5085 (merged) to 10.0 (GitLab 19.0) to avoid running into 19.0.x requires `global.psql.host`, while using... (#6521 - closed) when upgrading from 18.x.

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