fixed error with writing test data to opensearch

it's rather a workaround - the problem is caused by different "alert.metadata" field in different records and wrong auto-inferred schema which later cannot be converted, so I just modified the test data so the fields under "metadata" are always the same.

roles/nifi/templates/flow.xml.j2

@@ -9030,7 +9030,7 @@
                 <name>generate-ff-custom-text</name>
                 <value>[{"stream": 0,"flow": {"bytes_toserver": 74,"bytes_toclient": 0,"start": "${now():format('yyyy-MM-dd HH:mm:ss.SSS'):replaceFirst(' ','T')}","pkts_toserver": 1,"pkts_toclient": 0},"vlan": 665,"in_iface": "ens1f3","payload": "","timestamp": "${now():format('yyyy-MM-dd HH:mm:ss.SSS'):replaceFirst(' ','T')}","proto": "TCP","event_type": "alert","alert": {"category": "Not Suspicious Traffic","severity": 3,"action": "allowed","gid": 1,"signature_id": 29999991,"rev": 1,"signature": "SOC TEST1"},"payload_printable": "","source":{"ip":"10.${random():mod(254):plus(1)}.${random():mod(254):plus(1)}.${random():mod(254):plus(1)}","port": 43844},"destination":{"ip":"10.0.0.${random():mod(254):plus(1)}","port":"54323"},"host":"nifi.soctools.geant.org","host_domain":"geant.org"},
 {"timestamp":"${now():format('yyyy-MM-dd HH:mm:ss.SSS'):replaceFirst(' ','T')}","alert":{"action":"allowed","category":"Potentially Bad Traffic","gid":1,"metadata":{"affected_product":["Any"],"attack_target":["Client_Endpoint"],"created_at":["2019_07_26"],"deployment":["Perimeter"],"former_category":["DNS"],"signature_severity":["Minor"],"updated_at":["2019_09_28"]},"rev":3,"severity":2,"signature":"ET DNS Query for .cc TLD","signature_id":2027758},"app_proto":"dns","destination":{"ip":"10.10.10.${random():mod(254):plus(1)}","port":53},"dns":{"query":[{"id":37261,"rrname":"example.evil","rrtype":"A","tx_id":2,"type":"query"}]},"event_type":"alert","flow":{"bytes_toclient":1039,"bytes_toserver":343,"pkts_toclient":2,"pkts_toserver":3,"start":"${now():format('yyyy-MM-dd HH:mm:ss.SSS'):replaceFirst(' ','T')}"},"flow_id":1889254052511234,"in_iface":"if1","payload":"kY0BAAABAAAAAAABBnN0YXRpYwdhcmR1aW5vAmNjAAABAAEAACkPoAAAgAAAAA==","payload_printable":".............example.evil.......)........","proto":"UDP","source":{"ip":"10.${random():mod(254):plus(1)}.${random():mod(254):plus(1)}.${random():mod(254):plus(1)}","port":64164},"stream":0,"tx_id":2},
-{"timestamp":"${now():format('yyyy-MM-dd HH:mm:ss.SSS'):replaceFirst(' ','T')}","TLP":"AMBER","alert":{"action":"allowed","category":"Attempted Information Leak","gid":1,"metadata":{"created_at":["2014_10_15"],"former_category":["CURRENT_EVENTS"],"updated_at":["2014_10_15"]},"rev":6,"severity":2,"signature":"ET EXPLOIT SSL excessive fatal alerts (possible POODLE attack against server)","signature_id":2019418},"app_proto":"tls","destination":{"ip":"10.10.10.${random():mod(10):plus(1)}","port":37220},"event_type":"alert","flow":{"bytes_toclient":247,"bytes_toserver":298,"pkts_toclient":4,"pkts_toserver":4,"start":"${now():format('yyyy-MM-dd HH:mm:ss.SSS'):replaceFirst(' ','T')}"},"flow_id":43047386649621,"payload":"FQMAAAICKA==","payload_printable":"......(","proto":"TCP","source":{"ip":"10.${random():mod(254):plus(1)}.${random():mod(254):plus(1)}.${random():mod(254):plus(1)}","port":443},"stream":1,"tls":{"ja3":{},"version":"SSLv3"},"tx_id":0}]</value>
+{"timestamp":"${now():format('yyyy-MM-dd HH:mm:ss.SSS'):replaceFirst(' ','T')}","TLP":"AMBER","alert":{"action":"allowed","category":"Attempted Information Leak","gid":1,"metadata":{"affected_product":[],"attack_target":[],"created_at":["2014_10_15"],"deployment":[],"former_category":["CURRENT_EVENTS"],"signature_severity":[],"updated_at":["2014_10_15"]},"rev":6,"severity":2,"signature":"ET EXPLOIT SSL excessive fatal alerts (possible POODLE attack against server)","signature_id":2019418},"app_proto":"tls","destination":{"ip":"10.10.10.${random():mod(10):plus(1)}","port":37220},"event_type":"alert","flow":{"bytes_toclient":247,"bytes_toserver":298,"pkts_toclient":4,"pkts_toserver":4,"start":"${now():format('yyyy-MM-dd HH:mm:ss.SSS'):replaceFirst(' ','T')}"},"flow_id":43047386649621,"payload":"FQMAAAICKA==","payload_printable":"......(","proto":"TCP","source":{"ip":"10.${random():mod(254):plus(1)}.${random():mod(254):plus(1)}.${random():mod(254):plus(1)}","port":443},"stream":1,"tls":{"ja3":{},"version":"SSLv3"},"tx_id":0}]</value>
               </property>
               <property>
                 <name>character-set</name>