Add support for free-standing loki rules and grafana dashboards

[sed-i]

TODO:

• [x] change config items separator to underscore
• [x] provision grafana dashboards
• [x] tests

Depends on:

• [x] fetch-lib after
  • [x] https://github.com/canonical/prometheus-k8s-operator/pull/209
  • [x] https://github.com/canonical/prometheus-k8s-operator/pull/208
  • [x] https://github.com/canonical/loki-k8s-operator/pull/76
  • [x] https://github.com/canonical/grafana-k8s-operator/pull/53
  • [x] https://github.com/canonical/loki-k8s-operator/pull/79
  • [x] https://github.com/canonical/prometheus-k8s-operator/pull/210

[sed-i]

Recent changes to prom and loki broke integration tests. Reviews are welcome but addition fixes are probably coming up.