How to allow actors to export metrics when egress policy is enforced?

**Assumption:** metrics collection relies on gRPC h2c.

**Short-term solution:** Add the metrics collection address into the egress policy of every actor needing to export metrics. This can be tedious. A default egress policy in ActorTemplate https://github.com/agent-substrate/substrate/issues/1324 should help some. But if a Substrate cluster uses many different ActorTemplates, the metrics collection address needs to be added into all of them.

**Long-term solution:** Introduce a defaulting mechanism, which automatically adds the metrics collection address into the egress policy of every actor. This makes the assumption that every actor needs to export metrics, which may not hold.

cc @bowei @LiorLieberman @git286 @EItanya @keithmattix