[MM-52973] Avoid thundering herd problem in IsFirstUserAccount (#23549)

server/channels/app/platform/service.go

@@ -50,11 +50,13 @@ type PlatformService struct {
 	sessionCache  cache.Cache
 	sessionPool   sync.Pool
 
-	asymmetricSigningKey                   atomic.Pointer[ecdsa.PrivateKey]
-	clientConfig                           atomic.Value
-	clientConfigHash                       atomic.Value
-	limitedClientConfig                    atomic.Value
-	fetchUserCountForFirstUserAccountCheck atomic.Bool
+	asymmetricSigningKey atomic.Pointer[ecdsa.PrivateKey]
+	clientConfig         atomic.Value
+	clientConfigHash     atomic.Value
+	limitedClientConfig  atomic.Value
+
+	isFirstUserAccountLock sync.Mutex
+	isFirstUserAccount     atomic.Bool
 
 	logger              *mlog.Logger
 	notificationsLogger *mlog.Logger
@@ -129,7 +131,7 @@ func New(sc ServiceConfig, options ...Option) (*PlatformService, error) {
 	}
 
 	// Assume the first user account has not been created yet. A call to the DB will later check if this is really the case.
-	ps.fetchUserCountForFirstUserAccountCheck.Store(true)
+	ps.isFirstUserAccount.Store(true)
 
 	// Step 1: Cache provider.
 	// At the moment we only have this implementation