fix: allow custom admin user collection in query presets constraints (#12202)

Query preset "Specific User" constraints is currently fixed to `users`
collection. However, this will fail if one has a custom admin user collection.

packages/payload/src/query-presets/constraints.ts

@@ -74,7 +74,7 @@ export const getConstraints = (config: Config): Field => ({
                 },
               ],
             },
-            relationTo: 'users',
+            relationTo: config.admin?.user ?? 'users', // TODO: remove this fallback when the args are properly typed as `SanitizedConfig`
           },
           ...(config?.queryPresets?.constraints?.[operation]?.reduce(
             (acc: Field[], option: QueryPresetConstraint) => {