Add logging relation to kubeflow-volumes

[rgildein]

Use LogForwarder from loki_push_api library to forwards all logs from workload container to Loki. This requires to use ops 2.9 or newer, so it was needed to be updated.

fixes: #136

How I tested it:

# deployed the cos following https://charmhub.io/topics/canonical-observability-stack/tutorials/install-microk8s
$ tox -e integration -- --keep-models
$ juju switch test-charm-aosq
$ juju consume u1-k8s:cos.loki-logging 
Added u1-k8s:admin/cos.loki-logging as loki-logging
$ juju integrate grafana-agent-k8s loki-logging
$ kubectl get services -n test-charm-aosq | grep kubeflow-volumes
kubeflow-volumes-endpoints       ClusterIP      None             <none>        <none>                                  90m
kubeflow-volumes                 ClusterIP      10.152.183.49    <none>        5000/TCP                                90m 
$ curl 10.152.183.49:5000
...

And after checking the Grafana, I was able to see all logs.