Add marshalling to the metrics.Metrics package
Add marshalling to the metrics.Metrics package

This makes it easier for callers to serialize structs that contain
metrics. Callers do not have to convert the metrics to
map[string]interface{}.

Signed-off-by: Torin Sandall <933af5bec0bc58056526d55ca6c7b45fcf14cc48@gmail.com>

tsandall/opa,tsandall/opa,open-policy-agent/opa,open-policy-agent/opa,tsandall/opa,open-policy-agent/opa,open-policy-agent/opa,open-policy-agent/opa,tsandall/opa,open-policy-agent/opa,tsandall/opa,tsandall/opa