Update client.proto to include lease time left

Author: mangelajo

proto/jumpstarter/client/v1/client.proto

@@ -92,6 +92,7 @@ message Lease {
   optional google.protobuf.Timestamp effective_begin_time = 6 [(google.api.field_behavior) = OUTPUT_ONLY];
   optional google.protobuf.Timestamp end_time = 7;
   optional google.protobuf.Timestamp effective_end_time = 8 [(google.api.field_behavior) = OUTPUT_ONLY];
+  optional google.protobuf.Duration time_left = 12 [(google.api.field_behavior) = OUTPUT_ONLY];
   optional string client = 9 [
     (google.api.field_behavior) = OUTPUT_ONLY,
     (google.api.resource_reference) = {type: "jumpstarter.dev/Client"}