metropolis: rename KubernetesWorker to KubernetesController, add no-op KubernetesWorker

This is in preparation for actually splitting the Kubernetes service
into a control plane and data plane / worker. The new Worker service is
a no-op: it can be enabled/disabled, but has no practical effect.

Since we plan on keeping the control plane stuff mostly as is, and add
split worker functionality as a new codebase, it makes sense to rename
the existing role to Controller, and createa brand new Worker one (to
make future diffs smaller).

Change-Id: I79de3219f3c190d38469a0a8d7371820471c100d
Reviewed-on: https://review.monogon.dev/c/monogon/+/1325
Tested-by: Jenkins CI
Reviewed-by: Lorenz Brun <lorenz@monogon.tech>
diff --git a/metropolis/proto/api/management.proto b/metropolis/proto/api/management.proto
index 396df83..0df1d69 100644
--- a/metropolis/proto/api/management.proto
+++ b/metropolis/proto/api/management.proto
@@ -168,9 +168,11 @@
     string id = 4;
   }
 
-  // kubernetesWorker adjusts the appropriate role when set. Nodes performing
-  // this role must also be consensus members. 
+  // kubernetesController adjusts the appropriate role when set.
   optional bool kubernetesWorker = 2;
+  // kubernetesController adjusts the appropriate role when set. Nodes performing
+  // this role must also be consensus members.
+  optional bool kubernetesController = 5;
   optional bool consensusMember = 3;
 }