Improvements for conan2 build system

This documents several leftover improvements for the conan2 build system that remain after !625 (merged)

• Discovery of dependencies: The dependencies of the framework/library part of CORSIKA 8 are not saved/copied over to targets that depend on CORSIKA 8 (transitivity). They have to be listed again to properly build the downstream application.
• Using ${CONAN_CMAKE_DIR} in CMakeLists
• Writing in the source tree
• Writing in the source tree, part 2

added Build System label

assigned to @mreininghaus

mentioned in merge request !625 (merged)

created branch 685-improvements-for-conan2-build-system to address this issue

mentioned in merge request !632 (merged)

changed the description

marked the checklist item Writing in the source tree, part 2 as completed

created branch 685-improvements-for-conan2-build-system to address this issue

created branch 685-improvements-for-conan2-build-system-2 to address this issue

mentioned in merge request !635 (merged)

marked the checklist item Discovery of dependencies: The dependencies of the framework/library part of CORSIKA 8 are not saved/copied over to targets that depend on CORSIKA 8 (transitivity). They have to be listed again to properly build the downstream application. as completed