perf(group-fns): optimize sequential delete to be concurrent

backend/src/ee/services/group/group-fns.ts

@@ -336,8 +336,10 @@ export const removeUsersFromGroupByUserIds = async ({
         )
       );
 
-      // TODO: this part can be optimized
-      for await (const userId of userIds) {
+      const promises: Array<Promise<void>> = [];
+      for (const userId of userIds) {
+        promises.push(
+          (async () => {
             const t = await userGroupMembershipDAL.filterProjectsByUserMembership(userId, group.id, projectIds, tx);
             const projectsToDeleteKeyFor = projectIds.filter((p) => !t.has(p));
 
@@ -360,7 +362,10 @@ export const removeUsersFromGroupByUserIds = async ({
               },
               tx
             );
+          })()
+        );
       }
+      await Promise.all(promises);
     }
 
     if (membersToRemoveFromGroupPending.length) {