typesdb array specified in codec parameters

[stefws]

It would be nice whenever one specifies a typesdb array parameter to codec to somehow specify also include whatever is current default typesdb from the collectd plugin either before or after ones custom type, so one could avoid having to dubt default types which may change when updating plugin.
This way one could just have few local custom types in ones own path.

Eg.:
  codec => collectd { typesdb => ['load-default-typesdb', '/opt/logstash/custom/collect_types.db'] }
or
  codec => collectd { typesdb => ['/opt/logstash/custom/collect_types.db', 'load-default-typesdb'] }