Fix open/close/actuate trunk code and documentation

The OpenTrunk method was implemented as an alias for ActuateTrunk, but
the commands have different meanings in vehicles with powered trunks and
vehicles without. The implementations are now correct, and the proxied
`actuate_trunk` invokes ActuateTrunk, leaving its behavior unchanged.

pkg/protocol/error.go

@@ -51,6 +51,7 @@ var (
 	ErrProtocolNotSupported = errors.New("vehicle does not support protocol -- use REST API")
 	ErrRequiresBLE          = errors.New("command can only be sent over BLE")
 	ErrRequiresEncryption   = errors.New("command should not be sent in plaintext or encrypted with an unauthenticated public key")
+	ErrCommandNotSupported  = NewError("vehicle does not support this command", false, false)
 )
 
 type CommandError struct {

pkg/protocol/protobuf/vcsec.proto

@@ -19,7 +19,10 @@ message SignedMessage {
 }
 
 message ToVCSECMessage {
-    SignedMessage signedMessage = 1;
+    oneof sub_message {
+        SignedMessage signedMessage = 1;
+        UnsignedMessage unsignedMessage = 2;
+    }
 }
 
 message KeyIdentifier {
@@ -76,6 +79,10 @@ message InformationRequest {
 enum RKEAction_E {
     RKE_ACTION_UNLOCK = 0;
     RKE_ACTION_LOCK = 1;
+    RKE_ACTION_OPEN_TRUNK = 2;
+    RKE_ACTION_OPEN_FRUNK = 3;
+    RKE_ACTION_OPEN_CHARGE_PORT = 4;
+    RKE_ACTION_CLOSE_CHARGE_PORT = 5;
     RKE_ACTION_REMOTE_DRIVE       = 20;
     RKE_ACTION_AUTO_SECURE_VEHICLE = 29;
     RKE_ACTION_WAKE_VEHICLE = 30;