Attributes are not forwarded to NewRelic for logs

[mariusgrigaitis]

Logs in context integrations and newrelic-agent does not forward attributes from logs

https://docs.newrelic.com/docs/logs/logs-context/configure-logs-context-go/#installing-a-logs-in-context-plugin

https://github.com/newrelic/go-agent/blob/master/v3/integrations/logcontext-v2/nrslog/handler.go#L130

Expected Behavior

Attributes appear on NR.

Reproduction case

https://github.com/newrelic/go-agent/blob/master/v3/integrations/logcontext-v2/nrslog/example/main.go

Additional attributes can be added to prove the case in the linked example

Additional context

What's the point of integrating structured logging solutions into NewRelic if attributes (essential part of structured) are not being forwarded?

Seems to be the case for all logcontext-v2 integrations, since attributes are not part of logcontext-v2 design?

Related: #768