Expose Grafana & Set-up first alert (#232)

* Expose grafana & prometheus.

* Add grafana notifications.

* Don't expose prometheus, add brucke.link

* Add block difference graph.

* Fix dashboard.

* Add matrix notifications.

* Change the channel.

* Relay healthcheck (#228)

* Add Relay healthcheck.

* Use built-in healthcheck.

* Update to full URL.

* Fix URL and increase timeout.

* Fix default.

* show sccache

Co-authored-by: Denis S. Soldatov aka General-Beck <[email protected]>

* Disable alerts on no data.

* Tune external URL.

* Reduce scraping.

* Update access token during update.

* Add notification if there is no source blocks.

Co-authored-by: Denis S. Soldatov aka General-Beck <[email protected]>