Special plugin only to dump buffer contents to file

[tagomoris]

Many users are using out_file to dump buffer contents with <secondary> section when buffered output plugins are failing flush.
But out_file is too complex and with too many features for such purpose. We cannot assure anything if users use complex configuration in <secondary> section.

I propose a new plugin only for <secondary> section just to dump buffer contents to a path on local host, with just few, minimum # of options/parameters.

To be considered:

• Is it enough to support local disk only? any others?
• Can we re-format these records in any specific format to make it possible to extract/read dumped files by a utility command?