Add installation and packaging targets

[gufarui]

Gitlab Username: gufg

Summary

• Add full install rules so cpackexample, libcpackexamplelib, and headers land in ${CMAKE_INSTALL_PREFIX}/bin|lib|include/cpackexamplelib, and install README, MIT license (as copyright), a compressed Debian changelog, and a compressed man page.
• Introduce cmake/CPackConfig.cmake with maintainer/contact/vendor/description/homepage metadata, enable only TGZ and DEB generators, make the package stripped, and let CPACK_DEBIAN_PACKAGE_SHLIBDEPS derive dependencies.
• Provide Debian-specific docs (debian/changelog.Debian(.gz) and docs/cpackexample.1(.gz)) that satisfy lintian’s changelog/man checks so the .deb passes lintian (except the usual root warning).

Testing

1. docker run --rm --mount type=bind,source="$(pwd)",target=/mnt/cpack-exercise cpackexercise /bin/bash -lc "set -euo pipefail && cd /mnt/cpack-exercise && rm -rf build && cmake -S . -B build && cmake --build build && cmake --build build --target package"
2. tar -tzf build/cpackexample-0.1.0-Linux.tar.gz
3. dpkg-deb -c build/cpackexample_0.1.0-1_arm64.deb
4. docker run --rm --mount type=bind,source="$(pwd)",target=/mnt/cpack-exercise cpackexercise /bin/bash -lc "cd /mnt/cpack-exercise/build && apt-get -qq update && apt-get -y install ./cpackexample_0.1.0-1_arm64.deb && which cpackexample && cpackexample > /tmp/cpackexample.log && head -n 10 /tmp/cpackexample.log"
5. docker run --rm --mount type=bind,source="$(pwd)",target=/mnt/cpack-exercise cpackexercise /bin/bash -lc "cd /mnt/cpack-exercise/build && lintian ./cpackexample_0.1.0-1_arm64.deb"

lintian output:

running with root privileges is not recommended!