Install zstd in an alternate directory (#1172)

[jpsamper2009]

This prevents the compiled libzstd from being used by the host's cmake executable

Fixes #1172

[MichaelOrlov]

Hi JP @jpsamper2009 Thanks for the PR.
There are a compilation errors in rosbag2_compression_zstd package

-- stderr: rosbag2_compression_zstd
14:22:09 CMake Error at /usr/share/cmake-3.22/Modules/FindPackageHandleStandardArgs.cmake:230 (message):
14:22:09   Could NOT find zstd (missing: zstd_LIBRARY zstd_INCLUDE_DIR)
14:22:09 Call Stack (most recent call first):
14:22:09   /usr/share/cmake-3.22/Modules/FindPackageHandleStandardArgs.cmake:594 (_FPHSA_FAILURE_MESSAGE)
14:22:09   /tmp/ws/install_isolated/zstd_vendor/share/zstd_vendor/cmake/Modules/Findzstd.cmake:36 (find_package_handle_standard_args)
14:22:09   CMakeLists.txt:28 (find_package)
14:22:09 
14:22:09 
14:22:09 ---
14:22:09 Failed   <<< rosbag2_compression_zstd [1.48s, exited with code 1]

It looks like need to adjust path in zstd_vendor/cmake/Modules/Findzstd.cmake as well.