feat: add RemoveMachine API endpoint to remove a machine from the cluster

internal/machine/api/pb/cluster.proto

@@ -12,7 +12,7 @@ service Cluster {
   rpc AddMachine(AddMachineRequest) returns (AddMachineResponse);
   rpc ListMachines(google.protobuf.Empty) returns (ListMachinesResponse);
   rpc UpdateMachine(UpdateMachineRequest) returns (UpdateMachineResponse);
-  // TODO: add RemoveMachine (see stashed changes)
+  rpc RemoveMachine(RemoveMachineRequest) returns (google.protobuf.Empty);
 
   rpc ReserveDomain(ReserveDomainRequest) returns (Domain);
   rpc GetDomain(google.protobuf.Empty) returns (Domain);
@@ -51,6 +51,24 @@ message ListMachinesResponse {
   repeated MachineMember machines = 1;
 }
 
+message UpdateMachineRequest {
+  // Machine to update
+  string machine_id = 1;
+
+  // Updated machine information
+  optional string name = 2;
+  optional IP public_ip = 3;
+  repeated IPPort endpoints = 4;
+}
+
+message UpdateMachineResponse {
+  MachineInfo machine = 1;
+}
+
+message RemoveMachineRequest {
+  string id = 1;
+}
+
 message Domain {
   string name = 1;
 }
@@ -78,17 +96,3 @@ message DNSRecord {
   RecordType type = 2;
   repeated string values = 3;
 }
-
-message UpdateMachineRequest {
-  // Machine to update
-  string machine_id = 1;
-
-  // Updated machine information
-  optional string name = 2;
-  optional IP public_ip = 3;
-  repeated IPPort endpoints = 4;
-}
-
-message UpdateMachineResponse {
-  MachineInfo machine = 1;
-}