Add grafana opensearch datasource plugin

Adds the grafana opensearch datasource plugin to the grafana container
as this is currently missing and results in a error when trying to use
the plugin in grafana.

etc/kayobe/kolla.yml

@@ -350,7 +350,8 @@ kolla_build_blocks:
     ADD additions-archive /
   grafana_plugins_install: |
     RUN grafana-cli plugins install vonage-status-panel \
-        && grafana-cli plugins install grafana-piechart-panel
+        && grafana-cli plugins install grafana-piechart-panel \
+        && grafana-cli plugins install grafana-opensearch-datasource
   ironic_inspector_header: |
     ADD additions-archive /
   keystone_base_footer: |