write xmlrpc function getReleaseFlags that is to be contributed to the upstream.
Please refer to the following url for details on Bugzilla::RPC 2.18 functions mapped to upstream Bugzilla::WebService and for 2.18 xmlrpc functions sorted by percentage of calls: https://engineering.redhat.com/trac/bugzilla-3.0-rh/wiki/XmlrpcCrossComparison#a2.18xmlrpcfunctionssortedbypercentageofcalls
This function will not be ported to compat_xmlrpc temporary API as it is not
highly used and hasn't been requested by anyone.
Please reopen Bug if you think otherwise