[cento] - Additional fields for HTTP/DNS json export

Hi there, this is Andy Torres from Nagra.
As discussed we are in need of additional fields for HTTP/DNS available in cento json export.

HTTP
[NFv9 57832][IPFIX 35632.360][Len 4 varlen] %HTTP_METHOD HTTP METHOD
[NFv9 57653][IPFIX 35632.181][Len 2] %HTTP_RET_CODE HTTP return code (e.g. 200, 304...)
[NFv9 57654][IPFIX 35632.182][Len 128 varlen] %HTTP_REFERER HTTP Referer
[NFv9 57655][IPFIX 35632.183][Len 256 varlen] %HTTP_UA HTTP User Agent
[NFv9 57659][IPFIX 35632.187][Len 64 varlen] %HTTP_HOST HTTP(S) Host Name (IXIA Host Name)

DNS
[NFv9 57677][IPFIX 35632.205][Len 256 varlen] %DNS_QUERY DNS query
[NFv9 57679][IPFIX 35632.207][Len 1] %DNS_QUERY_TYPE DNS query type (e.g. 1=A, 2=NS..)
[NFv9 57680][IPFIX 35632.208][Len 1] %DNS_RET_CODE DNS return code (e.g. 0=no error)
[NFv9 57870][IPFIX 35632.398][Len 256 varlen] %DNS_RESPONSE DNS response(s)