Groups: use entity store for pending requests

app/soapbox/hooks/api/groups/useGroupMembershipRequests.ts

@@ -0,0 +1,13 @@
+import { Entities } from 'soapbox/entity-store/entities';
+import { useEntities } from 'soapbox/entity-store/hooks';
+import { accountSchema } from 'soapbox/schemas';
+
+function useGroupMembershipRequests(groupId: string) {
+  return useEntities(
+    [Entities.ACCOUNTS, 'membership_requests', groupId],
+    `/api/v1/groups/${groupId}/membership_requests`,
+    { schema: accountSchema },
+  );
+}
+
+export { useGroupMembershipRequests };