Allow users to provide custom `@prisma/client` location

In ODC, both the gateway and the core api use a generated prisma client. Because of the way `pnpm` links dependencies, generating the client in one of the two will override the other. We therefore have a special `@prisma/generated-client` location which is not a symlink. This is used for imports in each. However, attempting to import `@prisma/client` will fail at runtime, as it is not generated.