[context] Support config file option "proxy_auth_method", defaults "any"

Adds support for the "proxy_auth_method" configuration file option.
The default value is set to "any". Before that, the default
librepo/libcurl value "basic" was used.

Related to https://bugzilla.redhat.com/show_bug.cgi?id=1924001 .

libdnf/dnf-repo.cpp

@@ -1090,6 +1090,11 @@ dnf_repo_set_keyfile_data(DnfRepo *repo, gboolean reloadFromGKeyFile, GError **e
     if (!lr_handle_setopt(priv->repo_handle, error, LRO_PROXY, tmp_cstr))
         return FALSE;
 
+    // setup proxy authorization method
+    auto proxyAuthMethods = libdnf::Repo::Impl::stringToProxyAuthMethods(conf->proxy_auth_method().getValue());
+    if (!lr_handle_setopt(priv->repo_handle, error, LRO_PROXYAUTHMETHODS, static_cast<long>(proxyAuthMethods)))
+        return FALSE;
+
     // setup proxy username and password
     tmp_cstr = NULL;
     if (!conf->proxy_username().empty()) {