Update API definition file to include kotlin

Author: tusharkhandelwal8

firebase-config/api.txt

@@ -133,6 +133,7 @@ package com.google.firebase.remoteconfig {
   }
 
   public final class RemoteConfigKt {
+    method @NonNull public static com.google.firebase.remoteconfig.CustomSignals customSignals(@NonNull kotlin.jvm.functions.Function1<? super com.google.firebase.remoteconfig.CustomSignals.Builder,kotlin.Unit> builder);
     method @NonNull public static operator com.google.firebase.remoteconfig.FirebaseRemoteConfigValue get(@NonNull com.google.firebase.remoteconfig.FirebaseRemoteConfig, @NonNull String key);
     method @NonNull public static kotlinx.coroutines.flow.Flow<com.google.firebase.remoteconfig.ConfigUpdate> getConfigUpdates(@NonNull com.google.firebase.remoteconfig.FirebaseRemoteConfig);
     method @NonNull public static com.google.firebase.remoteconfig.FirebaseRemoteConfig getRemoteConfig(@NonNull com.google.firebase.Firebase);