repo: While cloning root metadata copy also metalink

Although metalink.xml is located out of repodata directory, it should be
cloned with repository metadata.
Without correct metalink.xml for example doesn't work package remote
location resolving (because mirrors stored in metalink.xml are unknown).

libdnf5/repo/repo.cpp

@@ -536,9 +536,13 @@ bool Repo::clone_root_metadata() {
     repo_cache.remove_solv_files();
 
     auto repodata_cachedir = std::filesystem::path(repo_cachedir) / CACHE_METADATA_DIR;
+    auto root_repodata_metalink = std::filesystem::path(root_repo_cachedir) / CACHE_METALINK_FILE;
     try {
         std::filesystem::create_directories(repodata_cachedir);
         std::filesystem::copy(root_repodata_cachedir, repodata_cachedir);
+        if (std::filesystem::exists(root_repodata_metalink)) {
+            std::filesystem::copy(root_repodata_metalink, repo_cachedir);
+        }
     } catch (const std::filesystem::filesystem_error & e) {
         logger.debug(
             "Error when cloning root repodata from \"{}\" to \"{}\" : \"{}\"",

libdnf5/repo/repo_cache.cpp

@@ -33,7 +33,6 @@ namespace {
 
 constexpr const char * CACHE_ATTRS_DIR = "attrs";
 constexpr const char * CACHE_MIRRORLIST_FILE = "mirrorlist";
-constexpr const char * CACHE_METALINK_FILE = "metalink.xml";
 
 
 // Removes a file or empty directory.

libdnf5/repo/repo_cache_private.hpp

@@ -33,6 +33,7 @@ namespace {
 constexpr const char * CACHE_METADATA_DIR = "repodata";
 constexpr const char * CACHE_PACKAGES_DIR = "packages";
 constexpr const char * CACHE_SOLV_FILES_DIR = "solv";
+constexpr const char * CACHE_METALINK_FILE = "metalink.xml";
 
 }  // namespace