Add dither to y2020 turret

Basically just duplicate what Austin did with the hood a while back.

Change-Id: I7df9a45056de1dfca878402013facd3349453825
Signed-off-by: James Kuszmaul <jabukuszmaul@gmail.com>
diff --git a/y2020/control_loops/superstructure/superstructure.h b/y2020/control_loops/superstructure/superstructure.h
index c03f7a7..e4a9cb6 100644
--- a/y2020/control_loops/superstructure/superstructure.h
+++ b/y2020/control_loops/superstructure/superstructure.h
@@ -28,6 +28,7 @@
   // voltage cap.
   static constexpr double kTurretFrictionGain = 10.0;
   static constexpr double kTurretFrictionVoltageLimit = 1.5;
+  static constexpr double kTurretDitherGain = 0.4;
 
   using PotAndAbsoluteEncoderSubsystem =
       ::frc971::control_loops::StaticZeroingSingleDOFProfiledSubsystem<