Increase NS record default TTLs to 3 hours

Per further discussion on b/130533696, we've decided to increase these so
tenants can have greater resilience to an outage in our DNS servers.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=248546853

java/google/registry/config/RegistryConfig.java

@@ -372,7 +372,7 @@ public final class RegistryConfig {
     @Provides
     @Config("dnsDefaultNsTtl")
     public static Duration provideDnsDefaultNsTtl() {
-      return Duration.standardHours(1);
+      return Duration.standardHours(3);
     }
 
     /**