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/prometheus.yml.pktpl.hcl

@@ -0,0 +1,34 @@
+# my global config
+global:
+  scrape_interval: 15s # Set the scrape interval to every 15 seconds. Default is every 1 minute.
+  evaluation_interval: 15s # Evaluate rules every 15 seconds. The default is every 1 minute.
+  # scrape_timeout is set to the global default (10s).
+
+# Prometheus DEUBG Port ${Vars.PrometheusPort}
+# Alertmanager configuration
+alerting:
+  alertmanagers:
+    - static_configs:
+        - targets:
+          # - alertmanager:9093
+
+# Load rules once and periodically evaluate them according to the global 'evaluation_interval'.
+rule_files:
+  # - "first_rules.yml"
+  # - "second_rules.yml"
+
+# A scrape configuration containing exactly one endpoint to scrape:
+# Here it's Prometheus itself.
+scrape_configs:
+%{ for scraper in Vars.Scrapers ~}
+  - job_name: "${scraper.Name}"
+    metrics_path: "${scraper.MetricsPath}"
+    scheme: "${scraper.Scheme}"
+
+    static_configs:
+      - targets:
+        %{ for target in scraper.Targets ~}
+        - "${target}"
+        %{endfor ~}
+
+%{ endfor ~}