rtl: implemented RTL based on cone shape

- user defines a cone half angle which defines the RTL altitude behavior
- if vehicle is outside the cone it will climb until it intersects the cone
and then return at this altitude.
- if vehicle is inside the cone or above the predefined return altitude (RTL_RETURN_ALT)
then it will return at the current altitude

Signed-off-by: RomanBapst <bapstroman@gmail.com>

src/modules/navigator/rtl_params.c

@@ -116,3 +116,16 @@ PARAM_DEFINE_FLOAT(RTL_MIN_DIST, 5.0f);
  * @group Return Mode
  */
 PARAM_DEFINE_INT32(RTL_TYPE, 0);
+
+/**
+ * Half-angle of the RTL cone.
+ *
+ * Defines the half-angle of the cone which defines the vehicle RTL behavior.
+ *
+ * @unit degrees
+ * @min 0
+ * @max 90
+ * @increment 1
+ * @group Return Mode
+ */
+PARAM_DEFINE_INT32(RTL_CONE_ANG, 30);