added capability to use elasticsearch datastreams

[jylitalo]

While taking kubernetes-event-explorer into use, I stumbled into an issue, where kubernetes-event-explorer logs:

{"level":"error","time":"2023-05-26T12:55:34Z","caller":"/app/pkg/sinks/elasticsearch.go:144","message":"Indexing failed: {"error":{"root_cause":[{"type":"mapper_parsing_exception","reason":"failed to parse"}],"type":"mapper_parsing_exception","reason":"failed to parse","caused_by":{"type":"illegal_argument_exception","reason":"data stream timestamp field [@timestamp] is missing"}},"status":400}"}

After looking for ways to fix this, I stumbled into opsgenie#165 and it solved the problem for my local build.