FeasibilityChecker: Add new TakeoffLandAvailable option

ADd a new misison feasiblity checker option to check if a proper landing approach is defined when in air. There must be at least a mission landing or a VTOL approach defined in order for the mission to be accepted. Else, use the same logic as in MIS_TKO_LAND_REQ=4

src/modules/navigator/mission_params.c

@@ -68,6 +68,7 @@ PARAM_DEFINE_FLOAT(MIS_TAKEOFF_ALT, 2.5f);
  * @value 2 Require a landing
  * @value 3 Require a takeoff and a landing
  * @value 4 Require both a takeoff and a landing, or neither
+ * @value 5 Same as previous, but require a landing if in air and no valid VTOL landing approach is present
  * @group Mission
  */
 PARAM_DEFINE_INT32(MIS_TKO_LAND_REQ, 0);