IMU: parameterize IMU integration time (IMU_INTEG_RATE)

- default integration rate now 200 Hz (5000 us interval)
 - set update rate for all drivers and simulators using PX4Accelerometer/PX4Gyroscope

src/modules/sensors/vehicle_imu/imu_parameters.c

@@ -0,0 +1,45 @@
+/****************************************************************************
+ *
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+
+/**
+* IMU integration rate.
+*
+* The rate at which raw IMU data is integrated to produce delta angles and delta velocities.
+*
+* @min 100
+* @max 1000
+* @unit Hz
+* @reboot_required true
+* @group Sensors
+*/
+PARAM_DEFINE_INT32(IMU_INTEG_RATE, 200);