FIX: allow changing default DNS query timeout of 2s via GlobalSetting (#20383)

The current default timeout is hardcoded to 2 seconds which is proving
too low for certain cases, and resulting in sporadic timeouts due to slow DNS queries.

lib/final_destination/resolver.rb

@@ -3,7 +3,8 @@
 class FinalDestination::Resolver
   @mutex = Mutex.new
   def self.lookup(addr, timeout: nil)
-    timeout ||= 2
+    timeout ||= default_dns_query_timeout
+
     @mutex.synchronize do
       @result = nil
 
@@ -36,6 +37,14 @@ class FinalDestination::Resolver
 
   private
 
+  def self.default_dns_query_timeout
+    if gs = GlobalSetting.dns_query_timeout_secs.presence
+      Integer(gs)
+    else
+      2
+    end
+  end
+
   def self.ensure_lookup_thread
     return if @thread&.alive?