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/common/common.proto b/metropolis/proto/common/common.proto
index ca4bfea..1c01834 100644
--- a/metropolis/proto/common/common.proto
+++ b/metropolis/proto/common/common.proto
@@ -28,6 +28,8 @@
 // can be used to carry required data to start up services for a given role,
 // this must not be confidential/private data.
 message NodeRoles {
+    message KubernetesController {
+    }
     message KubernetesWorker {
     }
     message ConsensusMember {
@@ -56,6 +58,7 @@
     }
     KubernetesWorker kubernetes_worker = 1;
     ConsensusMember consensus_member = 2;
+    KubernetesController kubernetes_controller = 3;
 }
 
 // NodeState is the state of a Metropolis node from the point of view of the