update the API definition file to include setCustomSignals

Author: tusharkhandelwal8

firebase-config/api.txt

@@ -35,6 +35,7 @@ package com.google.firebase.remoteconfig {
     method @NonNull public com.google.firebase.remoteconfig.FirebaseRemoteConfigValue getValue(@NonNull String);
     method @NonNull public com.google.android.gms.tasks.Task<java.lang.Void> reset();
     method @NonNull public com.google.android.gms.tasks.Task<java.lang.Void> setConfigSettingsAsync(@NonNull com.google.firebase.remoteconfig.FirebaseRemoteConfigSettings);
+    method @NonNull public com.google.android.gms.tasks.Task<java.lang.Void> setCustomSignals(@NonNull java.util.Map<java.lang.String,java.lang.Object>);
     method @NonNull public com.google.android.gms.tasks.Task<java.lang.Void> setDefaultsAsync(@NonNull java.util.Map<java.lang.String,java.lang.Object>);
     method @NonNull public com.google.android.gms.tasks.Task<java.lang.Void> setDefaultsAsync(@XmlRes int);
     field public static final boolean DEFAULT_VALUE_FOR_BOOLEAN = false;