Add standalone implementation

Add standalone implementation, giving a new choice to avoid using deprecated libgnome-keyring

src/unlock_keyrings.cc

@@ -44,6 +44,11 @@ int main(int argc, char **argv) {
             return 3;
         }
 
+#ifdef KEYRING_IMPL_standalone
+        rlog.warning("This implementation 'standalone' always unlocks your default keyring. Keyring name `{}` will be ignored. Build with KEYRING_IMPL=lib if necessary.", keyring_and_pswd.at(0));
+        keyring_and_pswd.at(0) = "_ignored_";
+#endif
+
         auto res = do_unlock(keyring_and_pswd.at(0), keyring_and_pswd.at(1));
         auto msg = keyringResultToString(res);
         if(res == GNOME_KEYRING_RESULT_OK)