parse_date use multiple pattern

[jalogisch]

Using parse_date is the only option to use if you have to work with exact times. flex_parse_date would could of provided micro seconds.

Having the option to provide multiple pattern that parse_date tries before it uses a default or does nothing would help to simplify the rules that need to be written to work with the _ standard_ syslog time.

let new_date = to_string($message.log_date);
let time = parse_date(
					value:new_date, 
					pattern:"MMM dd HH:mm:ss.SSS",
					pattern:"MMM dd HH:mm:ss ZZZ",
					pattern:"MMM dd HH:mm:ss.SSS ZZZ",
					timezone:"CET"
					);			
set_field("processed_time", time);

related to: #243

Environment

• Graylog Version: 2.4.3