Add a custom option page to WordPress Options

<?phpadd_action('admin_menu','register_parliamentary_dossier_settings_page');functionregister_parliamentary_dossier_settings_page(){add_submenu_page('options-general.php',__('Parliamentary Dossier Settings','astra-child'),__('Parliamentary Dossier','astra-child'),'manage_options','media-selector','parliamentary_dossier_settings_page_callback');}functionparliamentary_dossier_settings_page_callback(){if(isset($_POST['submit_image_selector'])&&isset($_POST['image_attachment_id'])){update_option('parliamentary_dossier_attachment_id',absint($_POST['image_attachment_id']));}wp_enqueue_media();printf('<h1>%1$s</h1><h2 style="font-size:20px;">%2$s</h2><form method="post"><div class="image-preview-wrapper"style="margin-bottom:15px;"><img id="image-preview"src="%3$s"height="400"></div><input id="upload_image_button"type="button"class="button"value="%4$s"/><input type="hidden"name="image_attachment_id"id="image_attachment_id"value="%5$s"><input type="submit"name="submit_image_selector"value="%6$s"class="button-primary"><p>%7$s</p></form>',esc_html__('Parliamentary Dossier','astra-child'),esc_html__('Frontpage Image','astra-child'),esc_html(wp_get_attachment_url(get_option('parliamentary_dossier_attachment_id'))),esc_html__('Upload image','astra-child'),esc_html(get_option('parliamentary_dossier_attachment_id')),esc_html__('Save','astra-child'),esc_html__('Recomended resolution:356x659.','astra-child'),);}add_action('admin_footer','parliamentary_dossier_print_scripts');functionparliamentary_dossier_print_scripts(){$my_saved_attachment_post_id=get_option('parliamentary_dossier_attachment_id',0);?><script type='text/javascript'>jQuery(document).ready(function($){varfile_frame;varwp_media_post_id=wp.media.model.settings.post.id;varset_to_post_id=<?phpecho$my_saved_attachment_post_id;?>jQuery('#upload_image_button').on('click',function(event){event.preventDefault();if(file_frame){file_frame.uploader.uploader.param('post_id',set_to_post_id);file_frame.open();return;}else{wp.media.model.settings.post.id=set_to_post_id;}file_frame=wp.media.frames.file_frame=wp.media({title:'Select a image to upload',button:{text:'Use this image',},multiple:!1});file_frame.on('select',function(){attachment=file_frame.state().get('selection').first().toJSON();$('#image-preview').attr('src',attachment.url).css('width','auto');$('#image_attachment_id').val(attachment.id);wp.media.model.settings.post.id=wp_media_post_id;});file_frame.open();});jQuery('a.add_media').on('click',function(){wp.media.model.settings.post.id=wp_media_post_id;});});</script><?php}