Add service account.

nix/kubernetes/keys/package/k8s-service-account/files/ca-config.json

@@ -0,0 +1,13 @@
+{
+  "signing": {
+    "default": {
+      "expiry": "8760h"
+    },
+    "profiles": {
+      "kubernetes": {
+        "usages": ["signing", "key encipherment", "server auth", "client auth"],
+        "expiry": "8760h"
+      }
+    }
+  }
+}