add config 'description'

Author: fagai

lib/embulk/output/bigquery.rb

@@ -63,6 +63,8 @@ def self.configure(config, schema, task_count)
           'payload_column'                 => config.param('payload_column',                 :string,  :default => nil),
           'payload_column_index'           => config.param('payload_column_index',           :integer, :default => nil),
 
+          'description'                    => config.param('description',                    :string,  :default => nil),
+
           'open_timeout_sec'               => config.param('open_timeout_sec',               :integer, :default => nil),
           'timeout_sec'                    => config.param('timeout_sec',                    :integer, :default => nil), # google-api-ruby-client < v0.11.0
           'send_timeout_sec'               => config.param('send_timeout_sec',               :integer, :default => nil), # google-api-ruby-client >= v0.11.0