Stabilize `service.peer.name` and `service.peer.namespace`

We (Java SIG) would like to take in the breaking change from `peer.service` to `service.peer.name` in the (somewhat) upcoming Java Instrumentation 3.0 release. It would help us to justify this breaking change if `service.peer.name` is marked as stable.

We don't have strong feelings about the new `service.peer.namespace`, but it seems to make sense to stabilize the pair together.