Add cos-agent support

[michaeldmitry]

Fixes #38
Fixes #30

Adds metrics scraping and charm tracing to parca-agent through cos_agent.

Context

Currently, the parca-agent snap doesn't expose a slot to access its logs.
parca-dev/parca-agent#3017

Testing Instructions

In a K8s model:
Deploy this bundle ((make sure to run juju run s3-integrator/leader sync-s3-credentials access-key=accesskey secret-key=mysoverysecretkey))

bundle: kubernetes
saas:
  remote-03c0779dfcc14a8587603554100dce99: {}
  remote-0d97fdf0fd1840548cfade97f254ca96: {}
applications:
  grafana:
    charm: grafana-k8s
    channel: latest/edge
    revision: 128
    base: [email protected]/stable
    resources:
      grafana-image: 70
      litestream-image: 45
    scale: 1
    constraints: arch=amd64
    storage:
      database: kubernetes,1,1024M
    trust: true
  loki:
    charm: loki-k8s
    channel: latest/edge
    revision: 184
    base: [email protected]/stable
    resources:
      loki-image: 100
      node-exporter-image: 3
    scale: 1
    constraints: arch=amd64
    storage:
      active-index-directory: kubernetes,1,1024M
      loki-chunks: kubernetes,1,1024M
    trust: true
  minio:
    charm: minio
    channel: ckf-1.9/edge
    revision: 383
    base: [email protected]/stable
    resources:
      oci-image: 545
    scale: 1
    options:
      access-key: accesskey
      secret-key: mysoverysecretkey
    constraints: arch=amd64
    storage:
      minio-data: kubernetes,1,10240M
    trust: true
  parca:
    charm: local:parca-k8s-1
    scale: 1
    constraints: arch=amd64
    storage:
      profiles: kubernetes,1,1024M
    trust: true
  prometheus:
    charm: prometheus-k8s
    channel: latest/edge
    revision: 226
    base: [email protected]/stable
    resources:
      prometheus-image: 151
    scale: 1
    constraints: arch=amd64
    storage:
      database: kubernetes,1,1024M
    trust: true
  s3-integrator:
    charm: s3-integrator
    channel: latest/edge
    revision: 97
    base: [email protected]/stable
    scale: 1
    options:
      bucket: tempo
      endpoint: minio-0.minio-endpoints.test.svc.cluster.local:9000
    constraints: arch=amd64
    trust: true
  tempo:
    charm: tempo-coordinator-k8s
    channel: latest/edge
    revision: 53
    base: [email protected]/stable
    resources:
      nginx-image: 5
      nginx-prometheus-exporter-image: 3
    scale: 1
    constraints: arch=amd64
    storage:
      data: kubernetes,1,1024M
    trust: true
  tempo-worker:
    charm: tempo-worker-k8s
    channel: latest/edge
    revision: 43
    base: [email protected]/stable
    resources:
      tempo-image: 4
    scale: 1
    constraints: arch=amd64
    storage:
      data: kubernetes,1,1024M
    trust: true
  traefik:
    charm: traefik-k8s
    channel: latest/edge
    revision: 226
    base: [email protected]/stable
    resources:
      traefik-image: 161
    scale: 1
    constraints: arch=amd64
    storage:
      configurations: kubernetes,1,1024M
    trust: true
relations:
- - tempo:s3
  - s3-integrator:s3-credentials
- - tempo:tempo-cluster
  - tempo-worker:tempo-cluster
- - tempo:ingress
  - traefik:traefik-route
- - loki:ingress
  - traefik:ingress-per-unit
- - prometheus:ingress
  - traefik:ingress-per-unit
- - grafana:ingress
  - traefik:traefik-route
- - grafana:grafana-source
  - loki:grafana-source
- - grafana:grafana-source
  - tempo:grafana-source
- - grafana:grafana-source
  - prometheus:grafana-source
- - parca:ingress
  - traefik:ingress
- - loki:logging
  - remote-03c0779dfcc14a8587603554100dce99:logging-consumer
- - prometheus:receive-remote-write
  - remote-03c0779dfcc14a8587603554100dce99:send-remote-write
- - tempo:tracing
  - remote-03c0779dfcc14a8587603554100dce99:tracing
- - parca:parca-store-endpoint
  - remote-0d97fdf0fd1840548cfade97f254ca96:parca-store-endpoint
--- # overlay.yaml
applications:
  loki:
    offers:
      loki:
        endpoints:
        - logging
        acl:
          admin: admin
  parca:
    offers:
      parca:
        endpoints:
        - parca-store-endpoint
        acl:
          admin: admin
  prometheus:
    offers:
      prometheus:
        endpoints:
        - receive-remote-write
        acl:
          admin: admin
  tempo:
    offers:
      tempo:
        endpoints:
        - tracing
        acl:
          admin: admin

In a machine model:
Deploy this bundle:

default-base: [email protected]/stable
saas:
  loki:
    url: micro:admin/test.loki
  parca:
    url: micro:admin/test.parca
  prometheus:
    url: micro:admin/test.prometheus
  tempo:
    url: micro:admin/test.tempo
applications:
  grafana-agent:
    charm: local:grafana-agent-2
    base: [email protected]/stable
  parca-agent:
    charm: local:parca-agent-8
    base: [email protected]/stable
  ubuntu:
    charm: ubuntu
    channel: latest/stable
    revision: 25
    num_units: 1
    to:
    - "2"
    constraints: arch=amd64
    storage:
      block: loop,100M
      files: rootfs,100M
machines:
  "2":
    constraints: virt-type=virtual-machine
relations:
- - ubuntu:juju-info
  - grafana-agent:juju-info
- - loki:logging
  - grafana-agent:logging-consumer
- - prometheus:receive-remote-write
  - grafana-agent:send-remote-write
- - tempo:tracing
  - grafana-agent:tracing
- - ubuntu:juju-info
  - parca-agent:juju-info
- - parca-agent:cos-agent
  - grafana-agent:cos-agent
- - parca-agent:parca-store-endpoint
  - parca:parca-store-endpoint

Then, open the grafana dashboard, you should see parca-agent metrics and charm traces in the prometheus and tempo DS.

[mmkay]

One comment, otherwise it looks fine :)