Move GPS blending from ekf2 to sensors module

- new sensors work item that subscribes to N x sensor_gps and publishes vehicle_gps_position
 - blending is now configurable with SENS_GPS_MASK and SENS_GPS_TAU

Co-authored-by: Jacob Crabill <jacob@volans-i.com>
Co-authored-by: Jacob Dahl <dahl.jakejacob@gmail.com>

msg/CMakeLists.txt

@@ -57,7 +57,6 @@ set(msg_files
 	distance_sensor.msg
 	ekf2_timestamps.msg
 	ekf_gps_drift.msg
-	ekf_gps_position.msg
 	esc_report.msg
 	esc_status.msg
 	estimator_innovations.msg
@@ -118,6 +117,7 @@ set(msg_files
 	sensor_baro.msg
 	sensor_combined.msg
 	sensor_correction.msg
+	sensor_gps.msg
 	sensor_gyro.msg
 	sensor_gyro_fifo.msg
 	sensor_mag.msg