Wait for drivetrain constants before starting

Otherwise we crash and confuse all sorts of things with a single bad
drivetrain status message...

Change-Id: Ib7a205c36393747a828650684725c61c0a914ad3
Signed-off-by: Austin Schuh <austin.linux@gmail.com>
diff --git a/y2023/control_loops/drivetrain/drivetrain_main.cc b/y2023/control_loops/drivetrain/drivetrain_main.cc
index b13e76f..eebae91 100644
--- a/y2023/control_loops/drivetrain/drivetrain_main.cc
+++ b/y2023/control_loops/drivetrain/drivetrain_main.cc
@@ -15,6 +15,8 @@
   aos::FlatbufferDetachedBuffer<aos::Configuration> config =
       aos::configuration::ReadConfig("aos_config.json");
 
+  frc971::constants::WaitForConstants<y2023::Constants>(&config.message());
+
   aos::ShmEventLoop event_loop(&config.message());
   std::unique_ptr<::frc971::control_loops::drivetrain::PuppetLocalizer>
       localizer = std::make_unique<