feat: add galera nodes

- add three nodes for a planned mariadb galera cluster

data/prodinf01n29.main.unkin.net.yaml

@@ -0,0 +1,4 @@
+---
+classes:
+  - roles::infra::metrics::sql::galera
+environment: testing

data/prodinf01n30.main.unkin.net.yaml

@@ -0,0 +1,4 @@
+---
+classes:
+  - roles::infra::metrics::sql::galera
+environment: testing

data/prodinf01n31.main.unkin.net.yaml

@@ -0,0 +1,4 @@
+---
+classes:
+  - roles::infra::metrics::sql::galera
+environment: testing