feat: promote `multiSchema` to GA; fix `multiSchema` introspection (#5563)
This PR:
- closes
[ORM-1172](https://linear.app/prisma-company/issue/ORM-1172/remove-multischema-preview-feature-flag)
- closes
[ORM-1279](https://linear.app/prisma-company/issue/ORM-1279/multischema-add-schema-attribute-on-introspected-tables)
- Removes the `multiSchema` preview feature flag and related
conditionals:
- Adjusts introspection tests
The multiSchema feature is now generally available without requiring a
preview feature flag.
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Co-authored-by: jkomyno <12381818+jkomyno@users.noreply.github.com>