Before this method just had some placeholder function that wasn't really
implementing the intended functionality of the conditional field
mapping. Now aggregations get also conditional field mapping
functionality.
When no field is present, use "count" , when field is present use "dc(field)". As described in the Sigma specifications.
Splunk throws errors when using "count()" with empy fields. use "count" instead.
Added dc() instead of count() when group-by field is present. Because count() doesn't do a distinct count in Splunk. Must be the dc() function instead.
Breaking change: Instead of feeding the output class with the results,
they are now returned as strings (*Backend.generate()) or list
(SigmaCollectionParser.generate()). Users of the library must now take
care of the output to the terminal, files or wherever Sigma rules should
be pushed to.
Mark McCurdy