Admin overview of the stores on the instance (#5745)

* Admin overview of the stores on the instance

POC/Draft for #5674.

* Enable admin to access foreign stores

* Remove stores list link

* UI updates

* Grant admins guest access to foreign stores

* Optimize cookie auth handler

* Test fix

* Revert changes related to StoreRepository.FindStore with isAdmin

BTCPayServer/Controllers/UIStoresController.cs

@@ -150,6 +150,7 @@ namespace BTCPayServer.Controllers
             {
                 return Forbid();
             }
+            HttpContext.SetStoreData(store);
             if (store.GetPermissionSet(userId).Contains(Policies.CanModifyStoreSettings, storeId))
             {
                 return RedirectToAction("Dashboard", new { storeId });
@@ -158,7 +159,6 @@ namespace BTCPayServer.Controllers
             {
                 return RedirectToAction("ListInvoices", "UIInvoice", new { storeId });
             }
-            HttpContext.SetStoreData(store);
             return View();
         }