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

Edited Sep 06, 2024 by Alan Coleman

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