Add charm tracing support

[mmkay]

Issue

This PR adds charm tracing support to alertmanager.

Testing Instructions

Use the following bundle:

bundle: kubernetes
applications:
  alertmanager-k8s:
    charm: local:alertmanager-k8s-0
    series: focal
    scale: 1
    constraints: arch=amd64
    storage:
      data: kubernetes,1,1024M
    trust: true
  grafana-k8s:
    charm: grafana-k8s
    channel: edge
    revision: 105
    series: focal
    resources:
      grafana-image: 67
      litestream-image: 43
    scale: 1
    constraints: arch=amd64
    storage:
      database: kubernetes,1,1024M
  self-signed-certificates:
    charm: self-signed-certificates
    channel: stable
    revision: 72
    scale: 1
    constraints: arch=amd64
  tempo-k8s:
    charm: tempo-k8s
    channel: edge
    revision: 27
    resources:
      tempo-image: 14
    scale: 1
    constraints: arch=amd64
    storage:
      data: kubernetes,1,1024M
  traefik-k8s:
    charm: traefik-k8s
    channel: edge
    revision: 170
    series: focal
    resources:
      traefik-image: 158
    scale: 1
    constraints: arch=amd64
    storage:
      configurations: kubernetes,1,1024M
relations:
- - tempo-k8s:grafana-source
  - grafana-k8s:grafana-source
- - grafana-k8s:ingress
  - traefik-k8s:traefik-route
- - self-signed-certificates:certificates
  - alertmanager-k8s:certificates
- - tempo-k8s:tracing
  - alertmanager-k8s:tracing
- - alertmanager-k8s:grafana-source
  - grafana-k8s:grafana-source
- - alertmanager-k8s:ingress
  - traefik-k8s:ingress
- - self-signed-certificates:certificates
  - grafana-k8s:certificates
- - self-signed-certificates:certificates
  - traefik-k8s:certificates