move hover_thrust_estimator to new module (mc_hover_thrust_estimator)

* MC_HTE: unitialize with hover_thrust parameter
* MC_HTE: constrain hover thrust setter between 0.1 and 0.9
* MC_HTE: integrate with land detector and velocity controller
* MCHoverThrustEstimator: Always publish an estimate even when not fusing measurements. This is required as the land detector and the position controller need to receive a hover thrust value.

* MC_HTE: use altitude agl threshold to start the estimator
local_position.z is relative to the origin of the EKF while dist_bottom
is above ground

Co-authored-by: bresch <brescianimathieu@gmail.com>

src/modules/mc_pos_control/mc_pos_control_params.c

@@ -73,6 +73,18 @@ PARAM_DEFINE_FLOAT(MPC_THR_MIN, 0.12f);
  */
 PARAM_DEFINE_FLOAT(MPC_THR_HOVER, 0.5f);
 
+/**
+ * Hover thrust source selector
+ *
+ * Set false to use the fixed parameter MPC_THR_HOVER
+ * (EXPERIMENTAL) Set true to use the value computed by the hover thrust estimator
+ *
+ * @boolean
+ * @category Developer
+ * @group Multicopter Position Control
+ */
+PARAM_DEFINE_INT32(MPC_USE_HTE, 0);
+
 /**
  * Thrust curve in Manual Mode
  *