libdnf5: Load plugins with RTLD_NODELETE flag set

Some plugins can use libraries, which have saved global data and unloading
such library can break this global data in a way which can cause a crash
of the daemon. One such library is glib, where this unload can break its
type system, with this shown on the dnf5daemon process console when it happens:

```
    (process:49835): GLib-GObject-CRITICAL **: 15:47:52.469: cannot register existing type 'AsMetadata'

    (process:49835): GLib-GObject-CRITICAL **: 15:47:52.469: cannot add private field to invalid (non-instantiatable) type '<invalid>'

    (process:49835): GLib-CRITICAL **: 15:47:52.469: g_once_init_leave_pointer: assertion 'result != 0' failed

    (process:49835): GLib-GObject-CRITICAL **: 15:47:52.469: g_object_new_with_properties: assertion 'G_TYPE_IS_OBJECT (object_type)' failed
    Segmentation fault (core dumped)
```

libdnf5/utils/library.cpp

@@ -26,7 +26,9 @@ along with libdnf.  If not, see <https://www.gnu.org/licenses/>.
 namespace libdnf5::utils {
 
 Library::Library(const std::string & path) : path(path) {
-    handle = dlopen(path.c_str(), RTLD_LAZY);
+    // the NODELETE is needed to not garbage plugin's libraries global data,
+    // like when the plugin uses glib, then it could break its type system
+    handle = dlopen(path.c_str(), RTLD_LAZY | RTLD_NODELETE);
     if (!handle) {
         const char * err_msg = dlerror();  // returns localized message, problem with later translation
         throw LibraryLoadingError(M_("Cannot load shared library \"{}\": {}"), path, std::string(err_msg));