fix(bootstraper): adding global variables support

Now we can declare "global" variables, in the "Globals" section the  the
configuration, this variables will be merged into the "Service"
variables and used in the templates. This how we share variables between
services.

data/templates/alertmanager.yml.pktpl.hcl

@@ -0,0 +1,16 @@
+route:
+  group_by: ['alertname']
+  group_wait: 30s
+  group_interval: 5m
+  repeat_interval: 1h
+  receiver: 'web.hook'
+receivers:
+  - name: 'web.hook'
+    webhook_configs:
+      - url: 'http://127.0.0.1:5001/'
+inhibit_rules:
+  - source_match:
+      severity: 'critical'
+    target_match:
+      severity: 'warning'
+    equal: ['alertname', 'dev', 'instance']