Modify the list of available views join plugins.
This hook may be used to modify plugin properties after they have been specified by other modules.
array $plugins: An array of all the existing plugin definitions, passed by reference.
\Drupal\views\Plugin\ViewsPluginManager
function hook_views_plugins_join_alter(array &$plugins) {
// Print out all join plugin names for debugging purposes.
debug($plugins);
}