Update vector-db to include postgresql

[rajsell]

Adding Azure PostgreSQL as an option for customers to use as a vector db

[learn-build-service-prod[bot]]

Learn Build status updates of commit 8d39c6b:

:white_check_mark: Validation status: passed

File	Status	Preview URL	Details
semantic-kernel/memories/vector-db.md	:white_check_mark:Succeeded

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