Add telemetry on the advertised bundle-URI capability

We already added some observability on the use of Bundle URI in #5649 (closed), but that reports how often the server tries to use bundle URI. But when the client doesn't have the bundle-uri capability enabled, the bundle URI won't be used.

Proposal

We already have stats.ReferenceDiscovery which captures the Caps, but that struct isn't used anywhere yet and those Caps are exported in any metric.

This is related to #5983 (closed), where want to export the existing metrics as well.