[feature] 'conan download': preserve tarfiles in the cache ('conan upload' to use it) #7869

As of Conan v1.30, the command conan download does extract the packaged file (conan_package.tgz) into the Conan cache to make it ready to use. As a consequence, conan upload needs to package the files again before uploading to a remote repository.

This workflow is used as a workaround to promote packages between different remote repositories, but it might modify the package revision if these operations happen in different machines (see #7760 (comment) for information related to symlinks changes).

The proposal is to keep any file downloaded from a remote repository (whenever Conan downloads a package or install it from a remote) and use the same tarfile if available in the conan upload command. Some sentinel should be able to notice if the files in the cache have been modified and the tarfile needs to be invalidated/removed and generated again.

Details TBD (maybe 2.0).- Does conan download actually extract the files or only when they are going to be used (conan install using the package)?

Side effect.- A workflow with conan download + conan upload will run much faster