Include Meta Box extension in themes/plugins

include-extension.php

<?php
require_once get_template_directory() . '/class-tgm-plugin-activation.php'; // Path to TGM Plugin Activation class.

add_action( 'tgmpa_register', 'your_prefix_register_required_plugins' );
function your_prefix_register_required_plugins() {
	/*
	 * Array of plugin arrays. Required keys are name and slug.
	 * If the source is NOT from the .org repo, then source is also required.
	 */
	$plugins = array(
		// This is an example of how to include a plugin bundled with a theme.
		array(
			'name'     => 'Extension Name', // The plugin name.
			'slug'     => 'extension-slug', // The plugin slug (typically the folder name).
			'source'   => get_stylesheet_directory() . '/lib/plugins/extension.zip', // The plugin source.
			'required' => true, // If false, the plugin is only 'recommended' instead of required.
		),
	);

	$config = array(
		'id'           => 'tgmpa',                 // Unique ID for hashing notices for multiple instances of TGMPA.
		'default_path' => '',                      // Default absolute path to bundled plugins.
		'menu'         => 'tgmpa-install-plugins', // Menu slug.
		'parent_slug'  => 'themes.php',            // Parent menu slug.
		'capability'   => 'edit_theme_options',    // Capability needed to view plugin install page, should be a capability associated with the parent menu used.
		'has_notices'  => true,                    // Show admin notices or not.
		'is_automatic' => false,                   // Automatically activate plugins after installation or not.
		'message'      => '',                      // Message to output right before the plugins table.
		'strings'      => array(
			'page_title' => __( 'Install Required Plugins', 'theme-slug' ),
			'menu_title'  => __( 'Install Plugins', 'theme-slug' ),
		)
	);

	tgmpa( $plugins, $config );

}