.maintain/sentry-node: Add monitoring to docker-compose stack (#5321)

* Substrate Dashboard example

* Improve README

* Update README_dashboard.md

* Add screenshots

* Minor fix

* Minor fix, image link

* .maintain/sentry-node: Add monitoring to docker-compose stack

With this patch a user can run the following fully configured and
monitored setup with a single command:

`docker-compose -f .maintain/sentry-node/docker-compose.yml up`

- 2 validators in two different network namespaces, connected via one
sentry node.

- Polkadot-js/apps to connect to one of the nodes above.

- Prometheus scraping the 3 Substrate nodes.

- Grafana displaying data from Prometheus with community dashboards

* .maintain/monitoring/grafana: Change default datasource name

* .maintain/monitoring/grafana: Add metric namespace option

* .maintain/monitoring/grafana: Remove `host` metric from most metrics

* .maintain/monitoring/grafana: Remove underscore from metric_namespace

* .maintain/monitoring: Use `instance` label instead of `hostname`

To identify a scrape target, one should use `instance` and not
`hostname` as multiple targets might run on the same node.

See https://prometheus.io/docs/concepts/jobs_instances/ for details.

* .maintain/monitoring: Introduce instance variable

* .maintain/monitoring/grafana: Rename substrate_block_height_number

* .maitain/monitoring/grafana: Use instance instead of host in legend

* .maintain/monitoring: Remove node exporter dependency

* .maintain/sentry-node/prometheus: Simplify configuration

* .maintain/monitoring/grafana: Update README and remove images

* .maintain/sentry-node: Improve docs

* .maintain/monitoring/grafana: Use metric_namespace template variable

* Use --sentry from v0.7.29 instead of a reserved-node

* .maintain/sentry-node: Revert sentry-a using validator-b as bootnode

Co-authored-by: DerFredy - @derfredy:matrix.org <derfredy@gmail.com>
Co-authored-by: david <davidd@custom.home>

substrate/.maintain/sentry-node/grafana/provisioning/datasources/datasource.yml

@@ -0,0 +1,50 @@
+# config file version
+apiVersion: 1
+
+# list of datasources that should be deleted from the database
+deleteDatasources:
+  - name: Prometheus
+    orgId: 1
+
+# list of datasources to insert/update depending
+# whats available in the database
+datasources:
+  # <string, required> name of the datasource. Required
+- name: Prometheus
+  # <string, required> datasource type. Required
+  type: prometheus
+  # <string, required> access mode. direct or proxy. Required
+  access: proxy
+  # <int> org id. will default to orgId 1 if not specified
+  orgId: 1
+  # <string> url
+  url: http://prometheus:9090
+  # <string> database password, if used
+  password:
+  # <string> database user, if used
+  user:
+  # <string> database name, if used
+  database:
+  # <bool> enable/disable basic auth
+  basicAuth: false
+  # <string> basic auth username, if used
+  basicAuthUser:
+  # <string> basic auth password, if used
+  basicAuthPassword:
+  # <bool> enable/disable with credentials headers
+  withCredentials:
+  # <bool> mark as default datasource. Max one per org
+  isDefault: true
+  # <map> fields that will be converted to json and stored in json_data
+  jsonData:
+     graphiteVersion: "1.1"
+     tlsAuth: false
+     tlsAuthWithCACert: false
+  # <string> json object of data that will be encrypted.
+  secureJsonData:
+    tlsCACert: "..."
+    tlsClientCert: "..."
+    tlsClientKey: "..."
+  version: 1
+  # <bool> allow users to edit datasources from the UI.
+  editable: true