[css-8220] COS lite integration (#17)

* [css-8220] cos lite integration with worker charm. 
* edit tox environment for formatting

CONTRIBUTING.md

@@ -17,7 +17,7 @@ pre-configured environments that can be used for linting and formatting code
 when you're preparing contributions to the charm:
 
 ```shell
-tox run -e format        # update your code according to linting rules
+tox run -e fmt        # update your code according to linting rules
 tox run -e lint          # code style
 tox run -e unit          # unit tests
 tox run -e integration   # integration tests

README.md

@@ -112,6 +112,39 @@ juju config temporal-worker-k8s sentry-release="1.0.0"
 juju config temporal-worker-k8s sentry-environment="staging"
 ```
 
+## Observability
+
+The Temporal worker operator charm can be related to the
+[Canonical Observability Stack](https://charmhub.io/topics/canonical-observability-stack)
+in order to collect logs and telemetry.
+To deploy cos-lite and expose its endpoints as offers, follow these steps:
+
+```bash
+# Deploy the cos-lite bundle:
+juju add-model cos
+juju deploy cos-lite --trust
+```
+
+```bash
+# Expose the cos integration endpoints:
+juju offer prometheus:metrics-endpoint
+juju offer loki:logging
+juju offer grafana:grafana-dashboard
+
+# Relate Temporal to the cos-lite apps:
+juju relate temporal-worker-k8s admin/cos.grafana
+juju relate temporal-worker-k8s admin/cos.loki
+juju relate temporal-worker-k8s admin/cos.prometheus
+```
+
+
+```bash
+# Access grafana with username "admin" and password:
+juju run grafana/0 -m cos get-admin-password --wait 1m
+# Grafana is listening on port 3000 of the app ip address.
+# Dashboard can be accessed under "Temporal Worker SDK Metrics", make sure to select the juju model which contains your Temporal worker operator charm.
+```
+
 ## Contributing
 
 This charm is still in active development. Please see the