Add default values for retryable response code

Signed-off-by: Shizuo Fujita <fujita@clear-code.com>

Author: Watson1978

lib/fluent/plugin/out_otlp.rb

@@ -32,7 +32,7 @@ class RetryableResponse < StandardError; end
       desc "Raise UnrecoverableError when the response is non success, 4xx/5xx"
       config_param :error_response_as_unrecoverable, :bool, default: true
       desc "The list of retryable response code"
-      config_param :retryable_response_codes, :array, value_type: :integer, default: nil
+      config_param :retryable_response_codes, :array, value_type: :integer, default: [429, 502, 503, 504]
 
       desc "Compress request body"
       config_param :compress, :enum, list: %i[text gzip], default: :text