Enable setting scrape_interval for DNS targets

Change-Id: I7c03add4e7e78110bdd874a118b493ce1af55655
Related-bug: PROD-27904 (PROD:27904)
diff --git a/prometheus/files/server/prometheus.yml b/prometheus/files/server/prometheus.yml
index 6722d5f..aaa6846 100644
--- a/prometheus/files/server/prometheus.yml
+++ b/prometheus/files/server/prometheus.yml
@@ -379,6 +379,9 @@
 
 {%- for name, endpoint in dns_endpoints | dictsort %}
   - job_name: {{ endpoint.name }}
+  {%- if endpoint.scrape_interval is defined %}
+    scrape_interval: {{ endpoint.scrape_interval }}
+  {%- endif %}
     dns_sd_configs:
     - names:
   {%- for domain in endpoint.domain %}