Add grafana dashboard

[Chris Johnston]

Currently we don't have the ability to collect and display metrics for etcd in grafana. It would be nice if a dashboard existed that would allow for displaying etcd metrics. This would greatly help with troubleshooting performance issues in etcd.

[Chris Johnston (cjohnston)]

From https://etcd.io/docs/v3.4.0/op-guide/monitoring/:

cat > /tmp/test-etcd.yaml <<EOF
global:
  scrape_interval: 10s
scrape_configs:
  - job_name: test-etcd
    static_configs:
    - targets: ['10.240.0.32:2379','10.240.0.33:2379','10.240.0.34:2379']
EOF
cat /tmp/test-etcd.yaml

https://github.com/etcd-io/etcd/blob/master/Documentation/op-guide/grafana.json

[Martin Kalcok (martin-kalcok)]

By default, etcd requires clients to authenticate with tls certificate signed by trusted CA when accessing the `/metrics` endpoint. I opened this bug https://bugs.launchpad.net/charm-prometheus2/+bug/1918277 in prometheus charm project which must be solved before this bug can proceed.

[Martin Kalcok (martin-kalcok)]

The situation with the prometheus charm dependency is actually the other way around. The prometheus functional tests need this change to be merged first. So after update of the PR with charmhelpers usage I marked it as ready for review.

PR: https://github.com/charmed-kubernetes/layer-etcd/pull/187

[Chris Johnston (cjohnston)]

Adding backport-needed as this is currently blocking other changes required.