Network check events should be kebab-case in JSON too

[RemiBardon]

When network checks are returned in JSON, events are not kebab-case as they should be. We should fix that.

 {
     "id": "SRV-c2s",
-    "event": "DnsRecordCheckResult",
+    "event": "dns-record-check-result",
     "data": {
         "description": "SRV record for client-to-server connections",
         "status": "INVALID"
     }
 }

It's true for all network checks individually and together.