[web] Promisify ensureAffiliationMiddleware and refactor InstitutionHubsController (#22242 feedback) (#22261)

* Promisify `ensureAffiliationMiddleware`

* In `ensureAffiliationMiddleware`, throw when UserNotFoundError

* Unnest object `_InstitutionHubsController`

* Format fix

GitOrigin-RevId: 5b3c6c24724520353540b8d8dd05005b6fa749ff

services/web/app/src/Features/User/UserController.js

@@ -202,7 +202,7 @@ async function ensureAffiliationMiddleware(req, res, next) {
   try {
     user = await UserGetter.promises.getUser(userId)
   } catch (error) {
-    return new Errors.UserNotFoundError({ info: { userId } })
+    throw new Errors.UserNotFoundError({ info: { userId } })
   }
   // if the user does not have permission to add an affiliation, we skip this middleware
   try {