metrics-generator metrics don't contain juju_ prefix in their labels

[michaeldmitry]

Bug Description

When enabling metrics-generator to generate span-based metrics, we inject juju toplogy into those metrics, but they get injected without juju_ prefix

To Reproduce

1- Deploy Tempo HA https://discourse.charmhub.io/t/topic/15489
2- Deploy prometheus-k8s
3- integrate coordinator with prometheus over remote-write-endpoint
4- Deploy grafana-k8s
5- integrate grafana and prometheus over grafana-source
6- open grafana dashboard
7- open sources and check metrics that start with span-, you'll see labels missing the prefix

Environment

microk8s 1.28
juju 3.5.4

Relevant log output

N/A

Additional context

No response

[michaeldmitry]

Should use label_matcher_dict