EKF2: Zero gyro update (#21691)

When at rest, directly fuse the gyro data as an observation of its bias.
This allows to strongly observe the gyro biases without having to fuse a
constant heading that makes the ekf too confident about its heading.

src/modules/ekf2/EKF/control.cpp

@@ -139,6 +139,7 @@ void Ekf::controlFusionModes(const imuSample &imu_delayed)
 	controlZeroInnovationHeadingUpdate();
 
 	controlZeroVelocityUpdate();
+	controlZeroGyroUpdate(imu_delayed);
 
 	// Fake position measurement for constraining drift when no other velocity or position measurements
 	controlFakePosFusion();