Merge branch 'hadox4prometheus' into 'master'

HA dox for prometheus

Closes platform-one/big-bang/apps/core/monitoring#97

See merge request platform-one/big-bang/bigbang!2323

docs/understanding-bigbang/package-architecture/monitoring.md

@@ -211,6 +211,31 @@ monitoring:
         replicas: 3
 ```
 
+#### Prometheus
+
+High Availability can be accomplished by increasing the number of replicas for the deployment of Prometheus. [Thanos](https://repo1.dso.mil/platform-one/big-bang/apps/sandbox/thanos/-/tree/main) must also be installed in the same namespace as the monitoring package in order for data to replicate across pods. An example of a Thanos object storage config using minIO [is located here](https://repo1.dso.mil/platform-one/big-bang/apps/sandbox/thanos/-/blob/main/tests/test-values.yaml). Thanos also supports cloud object storage endpoints.
+```yaml
+monitoring:
+  values:
+    thanosRuler:
+      enabled: true
+    prometheusOperator:
+      clusterDomain: "cluster.local"
+    prometheus:
+      thanosService:
+        enabled: true
+      thanosServiceMonitor:
+        enabled: true
+      prometheusSpec:
+        replicas: 3
+        thanos:
+          baseImage: registry1.dso.mil/ironbank/opensource/thanos/thanos
+          version: v0.29.0
+          objectStorageConfig:
+            key: objstore.yml
+            name: thanos-objstore-secret
+```
+
 #### Grafana
 
 High Availability can be accomplished by increasing the number of replicas for the deployment of Grafana and configuring an external database connection (postgresql/mysql) so users and dashboard information can be centrally located for the replicas to have a source of truth. See Grafana's [upstream documentation](https://grafana.com/docs/grafana/v9.0/setup-grafana/configure-grafana/#database)