Add timeout option to filters

I suggest a new optional `timeout` option be added to all filter plugins. Although not all filters would cleanly support being interrupted due to possible partial data updates, many filters would benefit from such an option without much change. Some filters go out to the network to do I/O and may take too long, etc.

both https://github.com/logstash-plugins/logstash-filter-grok/issues/82 and https://github.com/logstash-plugins/logstash-filter-grok/issues/65 discuss the need for a `timeout` option for the grok filter. I believe this feature is applicable to all plugins, not just Grok. All plugins may take too long for your liking.