Add CMake options to enable or disable installation of mujoco samples and simulate

[traversaro]

The current logic uses regular CMake variables, that create confusing behavior when a CMake cache variable with the same name is set from the command line. The PR does not change the behaviour of the build system, but permits to users to enable installation of simulate and samples executables from the CMake options.

[traversaro]

Unfortunatly, this can't work if we do not also duplicate the TargetAddRpath.cmake module in https://github.com/google-deepmind/mujoco/tree/7e87c6ac44ef980dbc5bb16f45100cd8b63c427b/sample/cmake and https://github.com/google-deepmind/mujoco/tree/7e87c6ac44ef980dbc5bb16f45100cd8b63c427b/simulate/cmake .

[traversaro]

Unfortunatly, this can't work if we do not also duplicate the TargetAddRpath.cmake module in https://github.com/google-deepmind/mujoco/tree/7e87c6ac44ef980dbc5bb16f45100cd8b63c427b/sample/cmake and https://github.com/google-deepmind/mujoco/tree/7e87c6ac44ef980dbc5bb16f45100cd8b63c427b/simulate/cmake .

Actually, we can make it work without duplication when MUJOCO_ENABLE_RPATH is OFF.

[traversaro]

Unfortunatly, this can't work if we do not also duplicate the TargetAddRpath.cmake module in https://github.com/google-deepmind/mujoco/tree/7e87c6ac44ef980dbc5bb16f45100cd8b63c427b/sample/cmake and https://github.com/google-deepmind/mujoco/tree/7e87c6ac44ef980dbc5bb16f45100cd8b63c427b/simulate/cmake .

Actually, we can make it work without duplication when MUJOCO_ENABLE_RPATH is OFF.

Fixed this in #1478, not sure why I can't reopen this PR.