Mercator: Add Manage Aliases link to Sites in sites.php. Save fil in wp-content/mu-plugins

mercator-add-manage-aliases-link.php

<?php
/**
  * Plugin Name: Mercator: Add Manage Aliases link to Sites in sites.php
  * Version: 0.1.0
  * Plugin URI: https://gist.github.com/soderlind/adce00cc8bb9fac9888982394fd5f114
  * Author: Per Soderind
  * Author URI: https://soderlind.no
  * Requires PHP: 7.0.0
  */

namespace Soderlind\MuPlugins;

add_filter( 'manage_sites_action_links', __NAMESPACE__ . '\\manage_domains_for_site', 10, 2 );

function manage_domains_for_site( $actions, $blog_id ) {

	if ( is_main_site( $blog_id ) ) {
		return $actions;
	}

	if ( ! is_mercator_enabled() ) {
		return $actions;
	}

	$mercator_alias_url = add_query_arg( 'id', $blog_id, network_admin_url( 'admin.php?action=mercator-aliases' ) );
	$actions            = array_merge(
		$actions, [
			'mercator_alias_url' => sprintf( '<a href="%s">%s</a>', $mercator_alias_url, __( 'Manage Aliases' ) ),
		]
	);
	return $actions;
}

function is_mercator_enabled() {
	return has_action( 'mercator_load' );
}