Use shelfmark type in SubjectNumber component

Found the type in the generated code. When possible we should use the
generated types because the prevent us from doing ts utility function
voodoo.

src/components/subject-number/SubjectNumber.tsx

@@ -1,10 +1,10 @@
 import * as React from "react";
 import { FC } from "react";
-import { Manifestation } from "../../core/utils/types/entities";
+import { Shelfmark } from "../../core/dbc-gateway/generated/graphql";
 
 export interface SubjectNumberProps {
   className?: string;
-  shelfmark: NonNullable<Manifestation["shelfmark"]>;
+  shelfmark: Shelfmark;
 }
 
 const SubjectNumber: FC<SubjectNumberProps> = ({