Add prometheus relay service

Set 2 replicas for prometheus server

Change-Id: I859195d5504d61511830899f2c28c92e24219585
diff --git a/.releasenotes/notes/add-prometheus-relay-df282e14ed88da8c.yaml b/.releasenotes/notes/add-prometheus-relay-df282e14ed88da8c.yaml
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+++ b/.releasenotes/notes/add-prometheus-relay-df282e14ed88da8c.yaml
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+---
+
+summary: >
+  Add prometheus relay service
+
+features:
+  - The Prometheus Relay service is responsible for
+    getting PromQL queries from external components,
+    such as Grafana, passing them to all discovered
+    Prometheus servers, merging the results and returning
+    the data. Prometheus Relay can be used to handle
+    Prometheus high availability or sharding.
diff --git a/.releasenotes/notes/spawn-multiple-replicas-prometheus-b80eaede9c19b8cd.yaml b/.releasenotes/notes/spawn-multiple-replicas-prometheus-b80eaede9c19b8cd.yaml
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+++ b/.releasenotes/notes/spawn-multiple-replicas-prometheus-b80eaede9c19b8cd.yaml
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+summary: >
+  Spawned two replicas of Prometheus to provide HA
+
+features:
+  - Spawned two replicas of Prometheus inside Docker Swarm.
+    These two instances have the same configuration file
+    and scrape the same endpoints. Therefore, they can be
+    treated as one-to-one copies.
+    Due to a limitation, when connecting to the Prometheus
+    web UI it is not possible to choose to which of the
+    existing Prometheus servers to connect and those
+    servers may contain slightly different results for the
+    same queries. Therefore, we suggest that you use Grafana
+    to visualize the data.