new PackageFlowFile processor

[Michael Moser]

Devs,

I can't find if this was suggested before, so here goes.  With the demise
of PostHTTP in NiFi 2.0, the recommended alternative is to MergeContent 1
file into FlowFile-v3 format then InvokeHTTP.  What does the community
think about supporting a new PackageFlowFile processor that is simple to
configure (compared to MergeContent!) and simply packages flowfile
attributes + content into a FlowFile-v[1,2,3] format?  This would also
offer a simple way to export flowfiles from NiFi that could later be
re-ingested and recovered using UnpackContent.  I don't want to submit a PR
for such a processor without first asking the community whether this would
be acceptable.

Thanks,
-- Mike