add base include directory to DJIOSDFConfig.cmake

[jcmonteiro]

Currently the generated DJIOSDKConfig.cmake does not add the base include directory to the DJIOSDK_INCLUDE_DIRS variable. This causes some programs which depend on the djiosdk to fail to compile, such as the DJI Onboard SDK ROS.

If the base include directory is not added to DJIOSDK_INCLUDE_DIRS, one cannot include headers as

#include <djiosdk/dji_vehicle.hpp>

Include is only possible via

#include <dji_vehicle.hpp>

In some cases, this bug might go unnoticed if one installs the djiosdk in a directory that is usually included by some other dependency, such as /usr/include.

I changed the DJIOSDKConfig.cmake to allow both include possibilities

#include <djiosdk/dji_vehicle.hpp>
#include <dji_vehicle.hpp>

to avoid compatibility issues.