kube/mirko: allow specifying securityContext

Change-Id: Iebafd6b1480ed1e1c1f3cf83361376987720766e

kube/mirko.libsonnet

@@ -103,6 +103,7 @@ local kube = import "kube.libsonnet";
                 main: cfg.container,
             }, 
             nodeSelector: null,
+            securityContext: {},
             container:: error "container(s) must be set",
             ports:: {
                 publicHTTP: {}, // name -> { port: no, dns: fqdn }
@@ -167,6 +168,7 @@ local kube = import "kube.libsonnet";
                         nodeSelector: cfg.nodeSelector,
 
                         serviceAccountName: component.sa.metadata.name,
+                        securityContext: cfg.securityContext,
                     },
                 },
             },