Fix serviceMonitorKubelet's metricRelabelings

Insert the metricRelabelings at the proper level.

Signed-off-by: Jetchko Jekov <jetchko.jekov@gmail.com>

jsonnet/custom-prometheus.jsonnet

@@ -27,6 +27,9 @@
   prometheus+:: {
     serviceMonitorKubelet+: {
       spec+: {
+        endpoints: std.map(function(endpoint)
+          if endpoint.port == "https-metrics" then
+            endpoint {
               metricRelabelings+: [
                 {
                   action: 'replace',
@@ -34,6 +37,11 @@
                   targetLabel: 'instance',
                 },
               ],
+            }
+          else
+            endpoint,
+          super.endpoints
+        ),
       },
     },
   },