Add support to send metrics with attributes and follow OLTP types

[ghazimuharam]

Summary

As the business metrics are easier to maintain, it would be helpful if we can push metrics with attributes using the go-agent lib, currently the RecordCustomMetric method only handle a single attribute metrics, and it get rid of the functionality such pushing gauge metrics with multiple category (unless we flatten the value into the metric name)

Desired Behaviour

Able to forward Metrics with custom attributes and OLTP types

Possible Solution

Additional context

As we tracking our transaction, there are possibilities where we need to monitor few of the business metrics depending on the transaction category, product, etc

[Newrelic-Boomi]

https://new-relic.atlassian.net/browse/NR-451379