Center Pagination rather than stretching to fill container width

Now that the Pagination component has a consistent width regardless of current
page, we can center it without causing the Prev/Next page buttons to move around
while navigating through pages. Previously the Pagination was stretched to fill
the parent, so that the Prev/Next buttons were aligned with the edges of the
table above.

h/static/scripts/group-forms/components/EditGroupMembersForm.tsx

@@ -397,7 +397,7 @@ export default function EditGroupMembersForm({
           </Scroll>
         </div>
         {typeof totalPages === 'number' && totalPages > 1 && (
-          <div className="mt-4">
+          <div className="mt-4 flex justify-center">
             <Pagination
               currentPage={pageIndex + 1}
               onChangePage={page => setPageIndex(page - 1)}