Support schema_update_options

[giwa]

schema_update_options (x)	array	optional	nil	(Experimental) List of ALLOW_FIELD_ADDITION or ALLOW_FIELD_RELAXATION or both. See jobs#configuration.load.schemaUpdateOptions. NOTE for the current status: schema_update_options does not work for copy job, that is, is not effective for most of modes such as append, replace and replace_backup. delete_in_advance deletes origin table so does not need to update schema. Only append_direct can utilize schema update.